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<div class="section" id="what-s-new-in-python-2-1">
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<h1>What’s New in Python 2.1<a class="headerlink" href="#what-s-new-in-python-2-1" title="Permalink to this headline">¶</a></h1>
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<dl class="field-list simple">
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<dt class="field-odd">Author</dt>
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<dd class="field-odd"><p>A.M. Kuchling</p>
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</dd>
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</dl>
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<div class="section" id="introduction">
|
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<h2>Introduction<a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
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<p>This article explains the new features in Python 2.1. While there aren’t as
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many changes in 2.1 as there were in Python 2.0, there are still some pleasant
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surprises in store. 2.1 is the first release to be steered through the use of
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Python Enhancement Proposals, or PEPs, so most of the sizable changes have
|
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accompanying PEPs that provide more complete documentation and a design
|
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rationale for the change. This article doesn’t attempt to document the new
|
||
features completely, but simply provides an overview of the new features for
|
||
Python programmers. Refer to the Python 2.1 documentation, or to the specific
|
||
PEP, for more details about any new feature that particularly interests you.</p>
|
||
<p>One recent goal of the Python development team has been to accelerate the pace
|
||
of new releases, with a new release coming every 6 to 9 months. 2.1 is the first
|
||
release to come out at this faster pace, with the first alpha appearing in
|
||
January, 3 months after the final version of 2.0 was released.</p>
|
||
<p>The final release of Python 2.1 was made on April 17, 2001.</p>
|
||
</div>
|
||
<div class="section" id="pep-227-nested-scopes">
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||
<h2>PEP 227: Nested Scopes<a class="headerlink" href="#pep-227-nested-scopes" title="Permalink to this headline">¶</a></h2>
|
||
<p>The largest change in Python 2.1 is to Python’s scoping rules. In Python 2.0,
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||
at any given time there are at most three namespaces used to look up variable
|
||
names: local, module-level, and the built-in namespace. This often surprised
|
||
people because it didn’t match their intuitive expectations. For example, a
|
||
nested recursive function definition doesn’t work:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">f</span><span class="p">():</span>
|
||
<span class="o">...</span>
|
||
<span class="k">def</span> <span class="nf">g</span><span class="p">(</span><span class="n">value</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
<span class="k">return</span> <span class="n">g</span><span class="p">(</span><span class="n">value</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span> <span class="o">+</span> <span class="mi">1</span>
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||
<span class="o">...</span>
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||
</pre></div>
|
||
</div>
|
||
<p>The function <code class="xref py py-func docutils literal notranslate"><span class="pre">g()</span></code> will always raise a <a class="reference internal" href="../library/exceptions.html#NameError" title="NameError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">NameError</span></code></a> exception, because
|
||
the binding of the name <code class="docutils literal notranslate"><span class="pre">g</span></code> isn’t in either its local namespace or in the
|
||
module-level namespace. This isn’t much of a problem in practice (how often do
|
||
you recursively define interior functions like this?), but this also made using
|
||
the <a class="reference internal" href="../reference/expressions.html#lambda"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">lambda</span></code></a> expression clumsier, and this was a problem in practice.
|
||
In code which uses <a class="reference internal" href="../reference/expressions.html#lambda"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">lambda</span></code></a> you can often find local variables being
|
||
copied by passing them as the default values of arguments.</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">find</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span>
|
||
<span class="s2">"Return list of any entries equal to 'name'"</span>
|
||
<span class="n">L</span> <span class="o">=</span> <span class="nb">filter</span><span class="p">(</span><span class="k">lambda</span> <span class="n">x</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="n">name</span><span class="p">:</span> <span class="n">x</span> <span class="o">==</span> <span class="n">name</span><span class="p">,</span>
|
||
<span class="bp">self</span><span class="o">.</span><span class="n">list_attribute</span><span class="p">)</span>
|
||
<span class="k">return</span> <span class="n">L</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>The readability of Python code written in a strongly functional style suffers
|
||
greatly as a result.</p>
|
||
<p>The most significant change to Python 2.1 is that static scoping has been added
|
||
to the language to fix this problem. As a first effect, the <code class="docutils literal notranslate"><span class="pre">name=name</span></code>
|
||
default argument is now unnecessary in the above example. Put simply, when a
|
||
given variable name is not assigned a value within a function (by an assignment,
|
||
or the <a class="reference internal" href="../reference/compound_stmts.html#def"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">def</span></code></a>, <a class="reference internal" href="../reference/compound_stmts.html#class"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">class</span></code></a>, or <a class="reference internal" href="../reference/simple_stmts.html#import"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">import</span></code></a> statements),
|
||
references to the variable will be looked up in the local namespace of the
|
||
enclosing scope. A more detailed explanation of the rules, and a dissection of
|
||
the implementation, can be found in the PEP.</p>
|
||
<p>This change may cause some compatibility problems for code where the same
|
||
variable name is used both at the module level and as a local variable within a
|
||
function that contains further function definitions. This seems rather unlikely
|
||
though, since such code would have been pretty confusing to read in the first
|
||
place.</p>
|
||
<p>One side effect of the change is that the <code class="docutils literal notranslate"><span class="pre">from</span> <span class="pre">module</span> <span class="pre">import</span> <span class="pre">*</span></code> and
|
||
<code class="docutils literal notranslate"><span class="pre">exec</span></code> statements have been made illegal inside a function scope under
|
||
certain conditions. The Python reference manual has said all along that <code class="docutils literal notranslate"><span class="pre">from</span>
|
||
<span class="pre">module</span> <span class="pre">import</span> <span class="pre">*</span></code> is only legal at the top level of a module, but the CPython
|
||
interpreter has never enforced this before. As part of the implementation of
|
||
nested scopes, the compiler which turns Python source into bytecodes has to
|
||
generate different code to access variables in a containing scope. <code class="docutils literal notranslate"><span class="pre">from</span>
|
||
<span class="pre">module</span> <span class="pre">import</span> <span class="pre">*</span></code> and <code class="docutils literal notranslate"><span class="pre">exec</span></code> make it impossible for the compiler to
|
||
figure this out, because they add names to the local namespace that are
|
||
unknowable at compile time. Therefore, if a function contains function
|
||
definitions or <a class="reference internal" href="../reference/expressions.html#lambda"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">lambda</span></code></a> expressions with free variables, the compiler
|
||
will flag this by raising a <a class="reference internal" href="../library/exceptions.html#SyntaxError" title="SyntaxError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SyntaxError</span></code></a> exception.</p>
|
||
<p>To make the preceding explanation a bit clearer, here’s an example:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">x</span> <span class="o">=</span> <span class="mi">1</span>
|
||
<span class="k">def</span> <span class="nf">f</span><span class="p">():</span>
|
||
<span class="c1"># The next line is a syntax error</span>
|
||
<span class="n">exec</span> <span class="s1">'x=2'</span>
|
||
<span class="k">def</span> <span class="nf">g</span><span class="p">():</span>
|
||
<span class="k">return</span> <span class="n">x</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Line 4 containing the <code class="docutils literal notranslate"><span class="pre">exec</span></code> statement is a syntax error, since
|
||
<code class="docutils literal notranslate"><span class="pre">exec</span></code> would define a new local variable named <code class="docutils literal notranslate"><span class="pre">x</span></code> whose value should
|
||
be accessed by <code class="xref py py-func docutils literal notranslate"><span class="pre">g()</span></code>.</p>
|
||
<p>This shouldn’t be much of a limitation, since <code class="docutils literal notranslate"><span class="pre">exec</span></code> is rarely used in
|
||
most Python code (and when it is used, it’s often a sign of a poor design
|
||
anyway).</p>
|
||
<p>Compatibility concerns have led to nested scopes being introduced gradually; in
|
||
Python 2.1, they aren’t enabled by default, but can be turned on within a module
|
||
by using a future statement as described in PEP 236. (See the following section
|
||
for further discussion of PEP 236.) In Python 2.2, nested scopes will become
|
||
the default and there will be no way to turn them off, but users will have had
|
||
all of 2.1’s lifetime to fix any breakage resulting from their introduction.</p>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt><span class="target" id="index-0"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0227"><strong>PEP 227</strong></a> - Statically Nested Scopes</dt><dd><p>Written and implemented by Jeremy Hylton.</p>
|
||
</dd>
|
||
</dl>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="pep-236-future-directives">
|
||
<h2>PEP 236: __future__ Directives<a class="headerlink" href="#pep-236-future-directives" title="Permalink to this headline">¶</a></h2>
|
||
<p>The reaction to nested scopes was widespread concern about the dangers of
|
||
breaking code with the 2.1 release, and it was strong enough to make the
|
||
Pythoneers take a more conservative approach. This approach consists of
|
||
introducing a convention for enabling optional functionality in release N that
|
||
will become compulsory in release N+1.</p>
|
||
<p>The syntax uses a <code class="docutils literal notranslate"><span class="pre">from...import</span></code> statement using the reserved module name
|
||
<a class="reference internal" href="../library/__future__.html#module-__future__" title="__future__: Future statement definitions"><code class="xref py py-mod docutils literal notranslate"><span class="pre">__future__</span></code></a>. Nested scopes can be enabled by the following statement:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">__future__</span> <span class="k">import</span> <span class="n">nested_scopes</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>While it looks like a normal <a class="reference internal" href="../reference/simple_stmts.html#import"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">import</span></code></a> statement, it’s not; there are
|
||
strict rules on where such a future statement can be put. They can only be at
|
||
the top of a module, and must precede any Python code or regular
|
||
<code class="xref std std-keyword docutils literal notranslate"><span class="pre">import</span></code> statements. This is because such statements can affect how
|
||
the Python bytecode compiler parses code and generates bytecode, so they must
|
||
precede any statement that will result in bytecodes being produced.</p>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt><span class="target" id="index-1"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0236"><strong>PEP 236</strong></a> - Back to the <a class="reference internal" href="../library/__future__.html#module-__future__" title="__future__: Future statement definitions"><code class="xref py py-mod docutils literal notranslate"><span class="pre">__future__</span></code></a></dt><dd><p>Written by Tim Peters, and primarily implemented by Jeremy Hylton.</p>
|
||
</dd>
|
||
</dl>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="pep-207-rich-comparisons">
|
||
<h2>PEP 207: Rich Comparisons<a class="headerlink" href="#pep-207-rich-comparisons" title="Permalink to this headline">¶</a></h2>
|
||
<p>In earlier versions, Python’s support for implementing comparisons on user-defined
|
||
classes and extension types was quite simple. Classes could implement a
|
||
<code class="xref py py-meth docutils literal notranslate"><span class="pre">__cmp__()</span></code> method that was given two instances of a class, and could only
|
||
return 0 if they were equal or +1 or -1 if they weren’t; the method couldn’t
|
||
raise an exception or return anything other than a Boolean value. Users of
|
||
Numeric Python often found this model too weak and restrictive, because in the
|
||
number-crunching programs that numeric Python is used for, it would be more
|
||
useful to be able to perform elementwise comparisons of two matrices, returning
|
||
a matrix containing the results of a given comparison for each element. If the
|
||
two matrices are of different sizes, then the compare has to be able to raise an
|
||
exception to signal the error.</p>
|
||
<p>In Python 2.1, rich comparisons were added in order to support this need.
|
||
Python classes can now individually overload each of the <code class="docutils literal notranslate"><span class="pre"><</span></code>, <code class="docutils literal notranslate"><span class="pre"><=</span></code>, <code class="docutils literal notranslate"><span class="pre">></span></code>,
|
||
<code class="docutils literal notranslate"><span class="pre">>=</span></code>, <code class="docutils literal notranslate"><span class="pre">==</span></code>, and <code class="docutils literal notranslate"><span class="pre">!=</span></code> operations. The new magic method names are:</p>
|
||
<table class="docutils align-center">
|
||
<colgroup>
|
||
<col style="width: 41%" />
|
||
<col style="width: 59%" />
|
||
</colgroup>
|
||
<thead>
|
||
<tr class="row-odd"><th class="head"><p>Operation</p></th>
|
||
<th class="head"><p>Method name</p></th>
|
||
</tr>
|
||
</thead>
|
||
<tbody>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre"><</span></code></p></td>
|
||
<td><p><a class="reference internal" href="../reference/datamodel.html#object.__lt__" title="object.__lt__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__lt__()</span></code></a></p></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre"><=</span></code></p></td>
|
||
<td><p><a class="reference internal" href="../reference/datamodel.html#object.__le__" title="object.__le__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__le__()</span></code></a></p></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">></span></code></p></td>
|
||
<td><p><a class="reference internal" href="../reference/datamodel.html#object.__gt__" title="object.__gt__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__gt__()</span></code></a></p></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">>=</span></code></p></td>
|
||
<td><p><a class="reference internal" href="../reference/datamodel.html#object.__ge__" title="object.__ge__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__ge__()</span></code></a></p></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">==</span></code></p></td>
|
||
<td><p><a class="reference internal" href="../reference/datamodel.html#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__eq__()</span></code></a></p></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">!=</span></code></p></td>
|
||
<td><p><a class="reference internal" href="../reference/datamodel.html#object.__ne__" title="object.__ne__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__ne__()</span></code></a></p></td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
<p>(The magic methods are named after the corresponding Fortran operators <code class="docutils literal notranslate"><span class="pre">.LT.</span></code>.
|
||
<code class="docutils literal notranslate"><span class="pre">.LE.</span></code>, &c. Numeric programmers are almost certainly quite familiar with
|
||
these names and will find them easy to remember.)</p>
|
||
<p>Each of these magic methods is of the form <code class="docutils literal notranslate"><span class="pre">method(self,</span> <span class="pre">other)</span></code>, where
|
||
<code class="docutils literal notranslate"><span class="pre">self</span></code> will be the object on the left-hand side of the operator, while
|
||
<code class="docutils literal notranslate"><span class="pre">other</span></code> will be the object on the right-hand side. For example, the
|
||
expression <code class="docutils literal notranslate"><span class="pre">A</span> <span class="pre"><</span> <span class="pre">B</span></code> will cause <code class="docutils literal notranslate"><span class="pre">A.__lt__(B)</span></code> to be called.</p>
|
||
<p>Each of these magic methods can return anything at all: a Boolean, a matrix, a
|
||
list, or any other Python object. Alternatively they can raise an exception if
|
||
the comparison is impossible, inconsistent, or otherwise meaningless.</p>
|
||
<p>The built-in <code class="docutils literal notranslate"><span class="pre">cmp(A,B)</span></code> function can use the rich comparison machinery,
|
||
and now accepts an optional argument specifying which comparison operation to
|
||
use; this is given as one of the strings <code class="docutils literal notranslate"><span class="pre">"<"</span></code>, <code class="docutils literal notranslate"><span class="pre">"<="</span></code>, <code class="docutils literal notranslate"><span class="pre">">"</span></code>, <code class="docutils literal notranslate"><span class="pre">">="</span></code>,
|
||
<code class="docutils literal notranslate"><span class="pre">"=="</span></code>, or <code class="docutils literal notranslate"><span class="pre">"!="</span></code>. If called without the optional third argument,
|
||
<code class="xref py py-func docutils literal notranslate"><span class="pre">cmp()</span></code> will only return -1, 0, or +1 as in previous versions of Python;
|
||
otherwise it will call the appropriate method and can return any Python object.</p>
|
||
<p>There are also corresponding changes of interest to C programmers; there’s a new
|
||
slot <code class="docutils literal notranslate"><span class="pre">tp_richcmp</span></code> in type objects and an API for performing a given rich
|
||
comparison. I won’t cover the C API here, but will refer you to PEP 207, or to
|
||
2.1’s C API documentation, for the full list of related functions.</p>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt><span class="target" id="index-2"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0207"><strong>PEP 207</strong></a> - Rich Comparisons</dt><dd><p>Written by Guido van Rossum, heavily based on earlier work by David Ascher, and
|
||
implemented by Guido van Rossum.</p>
|
||
</dd>
|
||
</dl>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="pep-230-warning-framework">
|
||
<h2>PEP 230: Warning Framework<a class="headerlink" href="#pep-230-warning-framework" title="Permalink to this headline">¶</a></h2>
|
||
<p>Over its 10 years of existence, Python has accumulated a certain number of
|
||
obsolete modules and features along the way. It’s difficult to know when a
|
||
feature is safe to remove, since there’s no way of knowing how much code uses it
|
||
— perhaps no programs depend on the feature, or perhaps many do. To enable
|
||
removing old features in a more structured way, a warning framework was added.
|
||
When the Python developers want to get rid of a feature, it will first trigger a
|
||
warning in the next version of Python. The following Python version can then
|
||
drop the feature, and users will have had a full release cycle to remove uses of
|
||
the old feature.</p>
|
||
<p>Python 2.1 adds the warning framework to be used in this scheme. It adds a
|
||
<a class="reference internal" href="../library/warnings.html#module-warnings" title="warnings: Issue warning messages and control their disposition."><code class="xref py py-mod docutils literal notranslate"><span class="pre">warnings</span></code></a> module that provide functions to issue warnings, and to filter
|
||
out warnings that you don’t want to be displayed. Third-party modules can also
|
||
use this framework to deprecate old features that they no longer wish to
|
||
support.</p>
|
||
<p>For example, in Python 2.1 the <code class="xref py py-mod docutils literal notranslate"><span class="pre">regex</span></code> module is deprecated, so importing
|
||
it causes a warning to be printed:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">regex</span>
|
||
<span class="go">__main__:1: DeprecationWarning: the regex module</span>
|
||
<span class="go"> is deprecated; please use the re module</span>
|
||
<span class="go">>>></span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Warnings can be issued by calling the <a class="reference internal" href="../library/warnings.html#warnings.warn" title="warnings.warn"><code class="xref py py-func docutils literal notranslate"><span class="pre">warnings.warn()</span></code></a> function:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">warnings</span><span class="o">.</span><span class="n">warn</span><span class="p">(</span><span class="s2">"feature X no longer supported"</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>The first parameter is the warning message; an additional optional parameters
|
||
can be used to specify a particular warning category.</p>
|
||
<p>Filters can be added to disable certain warnings; a regular expression pattern
|
||
can be applied to the message or to the module name in order to suppress a
|
||
warning. For example, you may have a program that uses the <code class="xref py py-mod docutils literal notranslate"><span class="pre">regex</span></code> module
|
||
and not want to spare the time to convert it to use the <a class="reference internal" href="../library/re.html#module-re" title="re: Regular expression operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code></a> module right
|
||
now. The warning can be suppressed by calling</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">warnings</span>
|
||
<span class="n">warnings</span><span class="o">.</span><span class="n">filterwarnings</span><span class="p">(</span><span class="n">action</span> <span class="o">=</span> <span class="s1">'ignore'</span><span class="p">,</span>
|
||
<span class="n">message</span><span class="o">=</span><span class="s1">'.*regex module is deprecated'</span><span class="p">,</span>
|
||
<span class="n">category</span><span class="o">=</span><span class="ne">DeprecationWarning</span><span class="p">,</span>
|
||
<span class="n">module</span> <span class="o">=</span> <span class="s1">'__main__'</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>This adds a filter that will apply only to warnings of the class
|
||
<a class="reference internal" href="../library/exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-class docutils literal notranslate"><span class="pre">DeprecationWarning</span></code></a> triggered in the <a class="reference internal" href="../library/__main__.html#module-__main__" title="__main__: The environment where the top-level script is run."><code class="xref py py-mod docutils literal notranslate"><span class="pre">__main__</span></code></a> module, and applies
|
||
a regular expression to only match the message about the <code class="xref py py-mod docutils literal notranslate"><span class="pre">regex</span></code> module
|
||
being deprecated, and will cause such warnings to be ignored. Warnings can also
|
||
be printed only once, printed every time the offending code is executed, or
|
||
turned into exceptions that will cause the program to stop (unless the
|
||
exceptions are caught in the usual way, of course).</p>
|
||
<p>Functions were also added to Python’s C API for issuing warnings; refer to PEP
|
||
230 or to Python’s API documentation for the details.</p>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt><span class="target" id="index-3"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0005"><strong>PEP 5</strong></a> - Guidelines for Language Evolution</dt><dd><p>Written by Paul Prescod, to specify procedures to be followed when removing old
|
||
features from Python. The policy described in this PEP hasn’t been officially
|
||
adopted, but the eventual policy probably won’t be too different from Prescod’s
|
||
proposal.</p>
|
||
</dd>
|
||
<dt><span class="target" id="index-4"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0230"><strong>PEP 230</strong></a> - Warning Framework</dt><dd><p>Written and implemented by Guido van Rossum.</p>
|
||
</dd>
|
||
</dl>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="pep-229-new-build-system">
|
||
<h2>PEP 229: New Build System<a class="headerlink" href="#pep-229-new-build-system" title="Permalink to this headline">¶</a></h2>
|
||
<p>When compiling Python, the user had to go in and edit the <code class="file docutils literal notranslate"><span class="pre">Modules/Setup</span></code>
|
||
file in order to enable various additional modules; the default set is
|
||
relatively small and limited to modules that compile on most Unix platforms.
|
||
This means that on Unix platforms with many more features, most notably Linux,
|
||
Python installations often don’t contain all useful modules they could.</p>
|
||
<p>Python 2.0 added the Distutils, a set of modules for distributing and installing
|
||
extensions. In Python 2.1, the Distutils are used to compile much of the
|
||
standard library of extension modules, autodetecting which ones are supported on
|
||
the current machine. It’s hoped that this will make Python installations easier
|
||
and more featureful.</p>
|
||
<p>Instead of having to edit the <code class="file docutils literal notranslate"><span class="pre">Modules/Setup</span></code> file in order to enable
|
||
modules, a <code class="file docutils literal notranslate"><span class="pre">setup.py</span></code> script in the top directory of the Python source
|
||
distribution is run at build time, and attempts to discover which modules can be
|
||
enabled by examining the modules and header files on the system. If a module is
|
||
configured in <code class="file docutils literal notranslate"><span class="pre">Modules/Setup</span></code>, the <code class="file docutils literal notranslate"><span class="pre">setup.py</span></code> script won’t attempt
|
||
to compile that module and will defer to the <code class="file docutils literal notranslate"><span class="pre">Modules/Setup</span></code> file’s
|
||
contents. This provides a way to specific any strange command-line flags or
|
||
libraries that are required for a specific platform.</p>
|
||
<p>In another far-reaching change to the build mechanism, Neil Schemenauer
|
||
restructured things so Python now uses a single makefile that isn’t recursive,
|
||
instead of makefiles in the top directory and in each of the <code class="file docutils literal notranslate"><span class="pre">Python/</span></code>,
|
||
<code class="file docutils literal notranslate"><span class="pre">Parser/</span></code>, <code class="file docutils literal notranslate"><span class="pre">Objects/</span></code>, and <code class="file docutils literal notranslate"><span class="pre">Modules/</span></code> subdirectories. This
|
||
makes building Python faster and also makes hacking the Makefiles clearer and
|
||
simpler.</p>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt><span class="target" id="index-5"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0229"><strong>PEP 229</strong></a> - Using Distutils to Build Python</dt><dd><p>Written and implemented by A.M. Kuchling.</p>
|
||
</dd>
|
||
</dl>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="pep-205-weak-references">
|
||
<h2>PEP 205: Weak References<a class="headerlink" href="#pep-205-weak-references" title="Permalink to this headline">¶</a></h2>
|
||
<p>Weak references, available through the <a class="reference internal" href="../library/weakref.html#module-weakref" title="weakref: Support for weak references and weak dictionaries."><code class="xref py py-mod docutils literal notranslate"><span class="pre">weakref</span></code></a> module, are a minor but
|
||
useful new data type in the Python programmer’s toolbox.</p>
|
||
<p>Storing a reference to an object (say, in a dictionary or a list) has the side
|
||
effect of keeping that object alive forever. There are a few specific cases
|
||
where this behaviour is undesirable, object caches being the most common one,
|
||
and another being circular references in data structures such as trees.</p>
|
||
<p>For example, consider a memoizing function that caches the results of another
|
||
function <code class="docutils literal notranslate"><span class="pre">f(x)</span></code> by storing the function’s argument and its result in a
|
||
dictionary:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">_cache</span> <span class="o">=</span> <span class="p">{}</span>
|
||
<span class="k">def</span> <span class="nf">memoize</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>
|
||
<span class="k">if</span> <span class="n">_cache</span><span class="o">.</span><span class="n">has_key</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>
|
||
<span class="k">return</span> <span class="n">_cache</span><span class="p">[</span><span class="n">x</span><span class="p">]</span>
|
||
|
||
<span class="n">retval</span> <span class="o">=</span> <span class="n">f</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
|
||
|
||
<span class="c1"># Cache the returned object</span>
|
||
<span class="n">_cache</span><span class="p">[</span><span class="n">x</span><span class="p">]</span> <span class="o">=</span> <span class="n">retval</span>
|
||
|
||
<span class="k">return</span> <span class="n">retval</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>This version works for simple things such as integers, but it has a side effect;
|
||
the <code class="docutils literal notranslate"><span class="pre">_cache</span></code> dictionary holds a reference to the return values, so they’ll
|
||
never be deallocated until the Python process exits and cleans up. This isn’t
|
||
very noticeable for integers, but if <code class="xref py py-func docutils literal notranslate"><span class="pre">f()</span></code> returns an object, or a data
|
||
structure that takes up a lot of memory, this can be a problem.</p>
|
||
<p>Weak references provide a way to implement a cache that won’t keep objects alive
|
||
beyond their time. If an object is only accessible through weak references, the
|
||
object will be deallocated and the weak references will now indicate that the
|
||
object it referred to no longer exists. A weak reference to an object <em>obj</em> is
|
||
created by calling <code class="docutils literal notranslate"><span class="pre">wr</span> <span class="pre">=</span> <span class="pre">weakref.ref(obj)</span></code>. The object being referred to is
|
||
returned by calling the weak reference as if it were a function: <code class="docutils literal notranslate"><span class="pre">wr()</span></code>. It
|
||
will return the referenced object, or <code class="docutils literal notranslate"><span class="pre">None</span></code> if the object no longer exists.</p>
|
||
<p>This makes it possible to write a <code class="xref py py-func docutils literal notranslate"><span class="pre">memoize()</span></code> function whose cache doesn’t
|
||
keep objects alive, by storing weak references in the cache.</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">_cache</span> <span class="o">=</span> <span class="p">{}</span>
|
||
<span class="k">def</span> <span class="nf">memoize</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>
|
||
<span class="k">if</span> <span class="n">_cache</span><span class="o">.</span><span class="n">has_key</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>
|
||
<span class="n">obj</span> <span class="o">=</span> <span class="n">_cache</span><span class="p">[</span><span class="n">x</span><span class="p">]()</span>
|
||
<span class="c1"># If weak reference object still exists,</span>
|
||
<span class="c1"># return it</span>
|
||
<span class="k">if</span> <span class="n">obj</span> <span class="ow">is</span> <span class="ow">not</span> <span class="kc">None</span><span class="p">:</span> <span class="k">return</span> <span class="n">obj</span>
|
||
|
||
<span class="n">retval</span> <span class="o">=</span> <span class="n">f</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
|
||
|
||
<span class="c1"># Cache a weak reference</span>
|
||
<span class="n">_cache</span><span class="p">[</span><span class="n">x</span><span class="p">]</span> <span class="o">=</span> <span class="n">weakref</span><span class="o">.</span><span class="n">ref</span><span class="p">(</span><span class="n">retval</span><span class="p">)</span>
|
||
|
||
<span class="k">return</span> <span class="n">retval</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>The <a class="reference internal" href="../library/weakref.html#module-weakref" title="weakref: Support for weak references and weak dictionaries."><code class="xref py py-mod docutils literal notranslate"><span class="pre">weakref</span></code></a> module also allows creating proxy objects which behave like
|
||
weak references — an object referenced only by proxy objects is deallocated –
|
||
but instead of requiring an explicit call to retrieve the object, the proxy
|
||
transparently forwards all operations to the object as long as the object still
|
||
exists. If the object is deallocated, attempting to use a proxy will cause a
|
||
<a class="reference internal" href="../library/weakref.html#weakref.ReferenceError" title="weakref.ReferenceError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">weakref.ReferenceError</span></code></a> exception to be raised.</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">proxy</span> <span class="o">=</span> <span class="n">weakref</span><span class="o">.</span><span class="n">proxy</span><span class="p">(</span><span class="n">obj</span><span class="p">)</span>
|
||
<span class="n">proxy</span><span class="o">.</span><span class="n">attr</span> <span class="c1"># Equivalent to obj.attr</span>
|
||
<span class="n">proxy</span><span class="o">.</span><span class="n">meth</span><span class="p">()</span> <span class="c1"># Equivalent to obj.meth()</span>
|
||
<span class="k">del</span> <span class="n">obj</span>
|
||
<span class="n">proxy</span><span class="o">.</span><span class="n">attr</span> <span class="c1"># raises weakref.ReferenceError</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt><span class="target" id="index-6"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0205"><strong>PEP 205</strong></a> - Weak References</dt><dd><p>Written and implemented by Fred L. Drake, Jr.</p>
|
||
</dd>
|
||
</dl>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="pep-232-function-attributes">
|
||
<h2>PEP 232: Function Attributes<a class="headerlink" href="#pep-232-function-attributes" title="Permalink to this headline">¶</a></h2>
|
||
<p>In Python 2.1, functions can now have arbitrary information attached to them.
|
||
People were often using docstrings to hold information about functions and
|
||
methods, because the <code class="docutils literal notranslate"><span class="pre">__doc__</span></code> attribute was the only way of attaching any
|
||
information to a function. For example, in the Zope Web application server,
|
||
functions are marked as safe for public access by having a docstring, and in
|
||
John Aycock’s SPARK parsing framework, docstrings hold parts of the BNF grammar
|
||
to be parsed. This overloading is unfortunate, since docstrings are really
|
||
intended to hold a function’s documentation; for example, it means you can’t
|
||
properly document functions intended for private use in Zope.</p>
|
||
<p>Arbitrary attributes can now be set and retrieved on functions using the regular
|
||
Python syntax:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">f</span><span class="p">():</span> <span class="k">pass</span>
|
||
|
||
<span class="n">f</span><span class="o">.</span><span class="n">publish</span> <span class="o">=</span> <span class="mi">1</span>
|
||
<span class="n">f</span><span class="o">.</span><span class="n">secure</span> <span class="o">=</span> <span class="mi">1</span>
|
||
<span class="n">f</span><span class="o">.</span><span class="n">grammar</span> <span class="o">=</span> <span class="s2">"A ::= B (C D)*"</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>The dictionary containing attributes can be accessed as the function’s
|
||
<a class="reference internal" href="../library/stdtypes.html#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__dict__</span></code></a>. Unlike the <a class="reference internal" href="../library/stdtypes.html#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__dict__</span></code></a> attribute of class instances, in
|
||
functions you can actually assign a new dictionary to <a class="reference internal" href="../library/stdtypes.html#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__dict__</span></code></a>, though
|
||
the new value is restricted to a regular Python dictionary; you <em>can’t</em> be
|
||
tricky and set it to a <code class="xref py py-class docutils literal notranslate"><span class="pre">UserDict</span></code> instance, or any other random object
|
||
that behaves like a mapping.</p>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt><span class="target" id="index-7"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0232"><strong>PEP 232</strong></a> - Function Attributes</dt><dd><p>Written and implemented by Barry Warsaw.</p>
|
||
</dd>
|
||
</dl>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="pep-235-importing-modules-on-case-insensitive-platforms">
|
||
<h2>PEP 235: Importing Modules on Case-Insensitive Platforms<a class="headerlink" href="#pep-235-importing-modules-on-case-insensitive-platforms" title="Permalink to this headline">¶</a></h2>
|
||
<p>Some operating systems have filesystems that are case-insensitive, MacOS and
|
||
Windows being the primary examples; on these systems, it’s impossible to
|
||
distinguish the filenames <code class="docutils literal notranslate"><span class="pre">FILE.PY</span></code> and <code class="docutils literal notranslate"><span class="pre">file.py</span></code>, even though they do store
|
||
the file’s name in its original case (they’re case-preserving, too).</p>
|
||
<p>In Python 2.1, the <a class="reference internal" href="../reference/simple_stmts.html#import"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">import</span></code></a> statement will work to simulate case-sensitivity
|
||
on case-insensitive platforms. Python will now search for the first
|
||
case-sensitive match by default, raising an <a class="reference internal" href="../library/exceptions.html#ImportError" title="ImportError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ImportError</span></code></a> if no such file
|
||
is found, so <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">file</span></code> will not import a module named <code class="docutils literal notranslate"><span class="pre">FILE.PY</span></code>.
|
||
Case-insensitive matching can be requested by setting the <span class="target" id="index-8"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONCASEOK"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONCASEOK</span></code></a>
|
||
environment variable before starting the Python interpreter.</p>
|
||
</div>
|
||
<div class="section" id="pep-217-interactive-display-hook">
|
||
<h2>PEP 217: Interactive Display Hook<a class="headerlink" href="#pep-217-interactive-display-hook" title="Permalink to this headline">¶</a></h2>
|
||
<p>When using the Python interpreter interactively, the output of commands is
|
||
displayed using the built-in <a class="reference internal" href="../library/functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code></a> function. In Python 2.1, the variable
|
||
<a class="reference internal" href="../library/sys.html#sys.displayhook" title="sys.displayhook"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.displayhook()</span></code></a> can be set to a callable object which will be called
|
||
instead of <a class="reference internal" href="../library/functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code></a>. For example, you can set it to a special
|
||
pretty-printing function:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="c1"># Create a recursive data structure</span>
|
||
<span class="gp">... </span><span class="n">L</span> <span class="o">=</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">]</span>
|
||
<span class="gp">>>> </span><span class="n">L</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">L</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">L</span> <span class="c1"># Show Python's default output</span>
|
||
<span class="go">[1, 2, 3, [...]]</span>
|
||
<span class="gp">>>> </span><span class="c1"># Use pprint.pprint() as the display function</span>
|
||
<span class="gp">... </span><span class="kn">import</span> <span class="nn">sys</span><span class="o">,</span> <span class="nn">pprint</span>
|
||
<span class="gp">>>> </span><span class="n">sys</span><span class="o">.</span><span class="n">displayhook</span> <span class="o">=</span> <span class="n">pprint</span><span class="o">.</span><span class="n">pprint</span>
|
||
<span class="gp">>>> </span><span class="n">L</span>
|
||
<span class="go">[1, 2, 3, <Recursion on list with id=135143996>]</span>
|
||
<span class="go">>>></span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt><span class="target" id="index-9"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0217"><strong>PEP 217</strong></a> - Display Hook for Interactive Use</dt><dd><p>Written and implemented by Moshe Zadka.</p>
|
||
</dd>
|
||
</dl>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="pep-208-new-coercion-model">
|
||
<h2>PEP 208: New Coercion Model<a class="headerlink" href="#pep-208-new-coercion-model" title="Permalink to this headline">¶</a></h2>
|
||
<p>How numeric coercion is done at the C level was significantly modified. This
|
||
will only affect the authors of C extensions to Python, allowing them more
|
||
flexibility in writing extension types that support numeric operations.</p>
|
||
<p>Extension types can now set the type flag <code class="docutils literal notranslate"><span class="pre">Py_TPFLAGS_CHECKTYPES</span></code> in their
|
||
<code class="docutils literal notranslate"><span class="pre">PyTypeObject</span></code> structure to indicate that they support the new coercion model.
|
||
In such extension types, the numeric slot functions can no longer assume that
|
||
they’ll be passed two arguments of the same type; instead they may be passed two
|
||
arguments of differing types, and can then perform their own internal coercion.
|
||
If the slot function is passed a type it can’t handle, it can indicate the
|
||
failure by returning a reference to the <code class="docutils literal notranslate"><span class="pre">Py_NotImplemented</span></code> singleton value.
|
||
The numeric functions of the other type will then be tried, and perhaps they can
|
||
handle the operation; if the other type also returns <code class="docutils literal notranslate"><span class="pre">Py_NotImplemented</span></code>, then
|
||
a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> will be raised. Numeric methods written in Python can also
|
||
return <code class="docutils literal notranslate"><span class="pre">Py_NotImplemented</span></code>, causing the interpreter to act as if the method
|
||
did not exist (perhaps raising a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>, perhaps trying another
|
||
object’s numeric methods).</p>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt><span class="target" id="index-10"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0208"><strong>PEP 208</strong></a> - Reworking the Coercion Model</dt><dd><p>Written and implemented by Neil Schemenauer, heavily based upon earlier work by
|
||
Marc-André Lemburg. Read this to understand the fine points of how numeric
|
||
operations will now be processed at the C level.</p>
|
||
</dd>
|
||
</dl>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="pep-241-metadata-in-python-packages">
|
||
<h2>PEP 241: Metadata in Python Packages<a class="headerlink" href="#pep-241-metadata-in-python-packages" title="Permalink to this headline">¶</a></h2>
|
||
<p>A common complaint from Python users is that there’s no single catalog of all
|
||
the Python modules in existence. T. Middleton’s Vaults of Parnassus at
|
||
<a class="reference external" href="http://www.vex.net/parnassus/">http://www.vex.net/parnassus/</a> are the largest catalog of Python modules, but
|
||
registering software at the Vaults is optional, and many people don’t bother.</p>
|
||
<p>As a first small step toward fixing the problem, Python software packaged using
|
||
the Distutils <strong class="command">sdist</strong> command will include a file named
|
||
<code class="file docutils literal notranslate"><span class="pre">PKG-INFO</span></code> containing information about the package such as its name,
|
||
version, and author (metadata, in cataloguing terminology). PEP 241 contains
|
||
the full list of fields that can be present in the <code class="file docutils literal notranslate"><span class="pre">PKG-INFO</span></code> file. As
|
||
people began to package their software using Python 2.1, more and more packages
|
||
will include metadata, making it possible to build automated cataloguing systems
|
||
and experiment with them. With the result experience, perhaps it’ll be possible
|
||
to design a really good catalog and then build support for it into Python 2.2.
|
||
For example, the Distutils <strong class="command">sdist</strong> and <strong class="command">bdist_*</strong> commands
|
||
could support an <code class="docutils literal notranslate"><span class="pre">upload</span></code> option that would automatically upload your
|
||
package to a catalog server.</p>
|
||
<p>You can start creating packages containing <code class="file docutils literal notranslate"><span class="pre">PKG-INFO</span></code> even if you’re not
|
||
using Python 2.1, since a new release of the Distutils will be made for users of
|
||
earlier Python versions. Version 1.0.2 of the Distutils includes the changes
|
||
described in PEP 241, as well as various bugfixes and enhancements. It will be
|
||
available from the Distutils SIG at <a class="reference external" href="https://www.python.org/community/sigs/current/distutils-sig/">https://www.python.org/community/sigs/current/distutils-sig/</a>.</p>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt><span class="target" id="index-11"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0241"><strong>PEP 241</strong></a> - Metadata for Python Software Packages</dt><dd><p>Written and implemented by A.M. Kuchling.</p>
|
||
</dd>
|
||
<dt><span class="target" id="index-12"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0243"><strong>PEP 243</strong></a> - Module Repository Upload Mechanism</dt><dd><p>Written by Sean Reifschneider, this draft PEP describes a proposed mechanism for
|
||
uploading Python packages to a central server.</p>
|
||
</dd>
|
||
</dl>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="new-and-improved-modules">
|
||
<h2>New and Improved Modules<a class="headerlink" href="#new-and-improved-modules" title="Permalink to this headline">¶</a></h2>
|
||
<ul>
|
||
<li><p>Ka-Ping Yee contributed two new modules: <code class="xref py py-mod docutils literal notranslate"><span class="pre">inspect.py</span></code>, a module for
|
||
getting information about live Python code, and <code class="xref py py-mod docutils literal notranslate"><span class="pre">pydoc.py</span></code>, a module for
|
||
interactively converting docstrings to HTML or text. As a bonus,
|
||
<code class="file docutils literal notranslate"><span class="pre">Tools/scripts/pydoc</span></code>, which is now automatically installed, uses
|
||
<code class="xref py py-mod docutils literal notranslate"><span class="pre">pydoc.py</span></code> to display documentation given a Python module, package, or
|
||
class name. For example, <code class="docutils literal notranslate"><span class="pre">pydoc</span> <span class="pre">xml.dom</span></code> displays the following:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">Python</span> <span class="n">Library</span> <span class="n">Documentation</span><span class="p">:</span> <span class="n">package</span> <span class="n">xml</span><span class="o">.</span><span class="n">dom</span> <span class="ow">in</span> <span class="n">xml</span>
|
||
|
||
<span class="n">NAME</span>
|
||
<span class="n">xml</span><span class="o">.</span><span class="n">dom</span> <span class="o">-</span> <span class="n">W3C</span> <span class="n">Document</span> <span class="n">Object</span> <span class="n">Model</span> <span class="n">implementation</span> <span class="k">for</span> <span class="n">Python</span><span class="o">.</span>
|
||
|
||
<span class="n">FILE</span>
|
||
<span class="o">/</span><span class="n">usr</span><span class="o">/</span><span class="n">local</span><span class="o">/</span><span class="n">lib</span><span class="o">/</span><span class="n">python2</span><span class="o">.</span><span class="mi">1</span><span class="o">/</span><span class="n">xml</span><span class="o">/</span><span class="n">dom</span><span class="o">/</span><span class="fm">__init__</span><span class="o">.</span><span class="n">pyc</span>
|
||
|
||
<span class="n">DESCRIPTION</span>
|
||
<span class="n">The</span> <span class="n">Python</span> <span class="n">mapping</span> <span class="n">of</span> <span class="n">the</span> <span class="n">Document</span> <span class="n">Object</span> <span class="n">Model</span> <span class="ow">is</span> <span class="n">documented</span> <span class="ow">in</span> <span class="n">the</span>
|
||
<span class="n">Python</span> <span class="n">Library</span> <span class="n">Reference</span> <span class="ow">in</span> <span class="n">the</span> <span class="n">section</span> <span class="n">on</span> <span class="n">the</span> <span class="n">xml</span><span class="o">.</span><span class="n">dom</span> <span class="n">package</span><span class="o">.</span>
|
||
|
||
<span class="n">This</span> <span class="n">package</span> <span class="n">contains</span> <span class="n">the</span> <span class="n">following</span> <span class="n">modules</span><span class="p">:</span>
|
||
<span class="o">...</span>
|
||
</pre></div>
|
||
</div>
|
||
<p><code class="file docutils literal notranslate"><span class="pre">pydoc</span></code> also includes a Tk-based interactive help browser. <code class="file docutils literal notranslate"><span class="pre">pydoc</span></code>
|
||
quickly becomes addictive; try it out!</p>
|
||
</li>
|
||
<li><p>Two different modules for unit testing were added to the standard library.
|
||
The <a class="reference internal" href="../library/doctest.html#module-doctest" title="doctest: Test pieces of code within docstrings."><code class="xref py py-mod docutils literal notranslate"><span class="pre">doctest</span></code></a> module, contributed by Tim Peters, provides a testing
|
||
framework based on running embedded examples in docstrings and comparing the
|
||
results against the expected output. PyUnit, contributed by Steve Purcell, is a
|
||
unit testing framework inspired by JUnit, which was in turn an adaptation of
|
||
Kent Beck’s Smalltalk testing framework. See <a class="reference external" href="http://pyunit.sourceforge.net/">http://pyunit.sourceforge.net/</a> for
|
||
more information about PyUnit.</p></li>
|
||
<li><p>The <a class="reference internal" href="../library/difflib.html#module-difflib" title="difflib: Helpers for computing differences between objects."><code class="xref py py-mod docutils literal notranslate"><span class="pre">difflib</span></code></a> module contains a class, <code class="xref py py-class docutils literal notranslate"><span class="pre">SequenceMatcher</span></code>, which
|
||
compares two sequences and computes the changes required to transform one
|
||
sequence into the other. For example, this module can be used to write a tool
|
||
similar to the Unix <strong class="program">diff</strong> program, and in fact the sample program
|
||
<code class="file docutils literal notranslate"><span class="pre">Tools/scripts/ndiff.py</span></code> demonstrates how to write such a script.</p></li>
|
||
<li><p><a class="reference internal" href="../library/curses.panel.html#module-curses.panel" title="curses.panel: A panel stack extension that adds depth to curses windows."><code class="xref py py-mod docutils literal notranslate"><span class="pre">curses.panel</span></code></a>, a wrapper for the panel library, part of ncurses and of
|
||
SYSV curses, was contributed by Thomas Gellekum. The panel library provides
|
||
windows with the additional feature of depth. Windows can be moved higher or
|
||
lower in the depth ordering, and the panel library figures out where panels
|
||
overlap and which sections are visible.</p></li>
|
||
<li><p>The PyXML package has gone through a few releases since Python 2.0, and Python
|
||
2.1 includes an updated version of the <a class="reference internal" href="../library/xml.html#module-xml" title="xml: Package containing XML processing modules"><code class="xref py py-mod docutils literal notranslate"><span class="pre">xml</span></code></a> package. Some of the
|
||
noteworthy changes include support for Expat 1.2 and later versions, the ability
|
||
for Expat parsers to handle files in any encoding supported by Python, and
|
||
various bugfixes for SAX, DOM, and the <code class="xref py py-mod docutils literal notranslate"><span class="pre">minidom</span></code> module.</p></li>
|
||
<li><p>Ping also contributed another hook for handling uncaught exceptions.
|
||
<a class="reference internal" href="../library/sys.html#sys.excepthook" title="sys.excepthook"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.excepthook()</span></code></a> can be set to a callable object. When an exception isn’t
|
||
caught by any <a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a>…<a class="reference internal" href="../reference/compound_stmts.html#except"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">except</span></code></a> blocks, the exception will be
|
||
passed to <a class="reference internal" href="../library/sys.html#sys.excepthook" title="sys.excepthook"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.excepthook()</span></code></a>, which can then do whatever it likes. At the
|
||
Ninth Python Conference, Ping demonstrated an application for this hook:
|
||
printing an extended traceback that not only lists the stack frames, but also
|
||
lists the function arguments and the local variables for each frame.</p></li>
|
||
<li><p>Various functions in the <a class="reference internal" href="../library/time.html#module-time" title="time: Time access and conversions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">time</span></code></a> module, such as <code class="xref py py-func docutils literal notranslate"><span class="pre">asctime()</span></code> and
|
||
<code class="xref py py-func docutils literal notranslate"><span class="pre">localtime()</span></code>, require a floating point argument containing the time in
|
||
seconds since the epoch. The most common use of these functions is to work with
|
||
the current time, so the floating point argument has been made optional; when a
|
||
value isn’t provided, the current time will be used. For example, log file
|
||
entries usually need a string containing the current time; in Python 2.1,
|
||
<code class="docutils literal notranslate"><span class="pre">time.asctime()</span></code> can be used, instead of the lengthier
|
||
<code class="docutils literal notranslate"><span class="pre">time.asctime(time.localtime(time.time()))</span></code> that was previously required.</p>
|
||
<p>This change was proposed and implemented by Thomas Wouters.</p>
|
||
</li>
|
||
<li><p>The <a class="reference internal" href="../library/ftplib.html#module-ftplib" title="ftplib: FTP protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">ftplib</span></code></a> module now defaults to retrieving files in passive mode,
|
||
because passive mode is more likely to work from behind a firewall. This
|
||
request came from the Debian bug tracking system, since other Debian packages
|
||
use <a class="reference internal" href="../library/ftplib.html#module-ftplib" title="ftplib: FTP protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">ftplib</span></code></a> to retrieve files and then don’t work from behind a firewall.
|
||
It’s deemed unlikely that this will cause problems for anyone, because Netscape
|
||
defaults to passive mode and few people complain, but if passive mode is
|
||
unsuitable for your application or network setup, call <code class="docutils literal notranslate"><span class="pre">set_pasv(0)</span></code> on
|
||
FTP objects to disable passive mode.</p></li>
|
||
<li><p>Support for raw socket access has been added to the <a class="reference internal" href="../library/socket.html#module-socket" title="socket: Low-level networking interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">socket</span></code></a> module,
|
||
contributed by Grant Edwards.</p></li>
|
||
<li><p>The <a class="reference internal" href="../library/profile.html#module-pstats" title="pstats: Statistics object for use with the profiler."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pstats</span></code></a> module now contains a simple interactive statistics browser
|
||
for displaying timing profiles for Python programs, invoked when the module is
|
||
run as a script. Contributed by Eric S. Raymond.</p></li>
|
||
<li><p>A new implementation-dependent function, <code class="docutils literal notranslate"><span class="pre">sys._getframe([depth])</span></code>, has
|
||
been added to return a given frame object from the current call stack.
|
||
<a class="reference internal" href="../library/sys.html#sys._getframe" title="sys._getframe"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys._getframe()</span></code></a> returns the frame at the top of the call stack; if the
|
||
optional integer argument <em>depth</em> is supplied, the function returns the frame
|
||
that is <em>depth</em> calls below the top of the stack. For example,
|
||
<code class="docutils literal notranslate"><span class="pre">sys._getframe(1)</span></code> returns the caller’s frame object.</p>
|
||
<p>This function is only present in CPython, not in Jython or the .NET
|
||
implementation. Use it for debugging, and resist the temptation to put it into
|
||
production code.</p>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
<div class="section" id="other-changes-and-fixes">
|
||
<h2>Other Changes and Fixes<a class="headerlink" href="#other-changes-and-fixes" title="Permalink to this headline">¶</a></h2>
|
||
<p>There were relatively few smaller changes made in Python 2.1 due to the shorter
|
||
release cycle. A search through the CVS change logs turns up 117 patches
|
||
applied, and 136 bugs fixed; both figures are likely to be underestimates. Some
|
||
of the more notable changes are:</p>
|
||
<ul>
|
||
<li><p>A specialized object allocator is now optionally available, that should be
|
||
faster than the system <code class="xref py py-func docutils literal notranslate"><span class="pre">malloc()</span></code> and have less memory overhead. The
|
||
allocator uses C’s <code class="xref py py-func docutils literal notranslate"><span class="pre">malloc()</span></code> function to get large pools of memory, and
|
||
then fulfills smaller memory requests from these pools. It can be enabled by
|
||
providing the <code class="xref std std-option docutils literal notranslate"><span class="pre">--with-pymalloc</span></code> option to the <strong class="program">configure</strong>
|
||
script; see <code class="file docutils literal notranslate"><span class="pre">Objects/obmalloc.c</span></code> for the implementation details.</p>
|
||
<p>Authors of C extension modules should test their code with the object allocator
|
||
enabled, because some incorrect code may break, causing core dumps at runtime.
|
||
There are a bunch of memory allocation functions in Python’s C API that have
|
||
previously been just aliases for the C library’s <code class="xref py py-func docutils literal notranslate"><span class="pre">malloc()</span></code> and
|
||
<code class="xref py py-func docutils literal notranslate"><span class="pre">free()</span></code>, meaning that if you accidentally called mismatched functions, the
|
||
error wouldn’t be noticeable. When the object allocator is enabled, these
|
||
functions aren’t aliases of <code class="xref py py-func docutils literal notranslate"><span class="pre">malloc()</span></code> and <code class="xref py py-func docutils literal notranslate"><span class="pre">free()</span></code> any more, and
|
||
calling the wrong function to free memory will get you a core dump. For
|
||
example, if memory was allocated using <code class="xref py py-func docutils literal notranslate"><span class="pre">PyMem_New()</span></code>, it has to be freed
|
||
using <code class="xref py py-func docutils literal notranslate"><span class="pre">PyMem_Del()</span></code>, not <code class="xref py py-func docutils literal notranslate"><span class="pre">free()</span></code>. A few modules included with Python
|
||
fell afoul of this and had to be fixed; doubtless there are more third-party
|
||
modules that will have the same problem.</p>
|
||
<p>The object allocator was contributed by Vladimir Marangozov.</p>
|
||
</li>
|
||
<li><p>The speed of line-oriented file I/O has been improved because people often
|
||
complain about its lack of speed, and because it’s often been used as a naïve
|
||
benchmark. The <a class="reference internal" href="../library/readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><code class="xref py py-meth docutils literal notranslate"><span class="pre">readline()</span></code></a> method of file objects has therefore been
|
||
rewritten to be much faster. The exact amount of the speedup will vary from
|
||
platform to platform depending on how slow the C library’s <code class="xref py py-func docutils literal notranslate"><span class="pre">getc()</span></code> was, but
|
||
is around 66%, and potentially much faster on some particular operating systems.
|
||
Tim Peters did much of the benchmarking and coding for this change, motivated by
|
||
a discussion in comp.lang.python.</p>
|
||
<p>A new module and method for file objects was also added, contributed by Jeff
|
||
Epler. The new method, <code class="xref py py-meth docutils literal notranslate"><span class="pre">xreadlines()</span></code>, is similar to the existing
|
||
<code class="xref py py-func docutils literal notranslate"><span class="pre">xrange()</span></code> built-in. <code class="xref py py-func docutils literal notranslate"><span class="pre">xreadlines()</span></code> returns an opaque sequence object
|
||
that only supports being iterated over, reading a line on every iteration but
|
||
not reading the entire file into memory as the existing <code class="xref py py-meth docutils literal notranslate"><span class="pre">readlines()</span></code> method
|
||
does. You’d use it like this:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">sys</span><span class="o">.</span><span class="n">stdin</span><span class="o">.</span><span class="n">xreadlines</span><span class="p">():</span>
|
||
<span class="c1"># ... do something for each line ...</span>
|
||
<span class="o">...</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>For a fuller discussion of the line I/O changes, see the python-dev summary for
|
||
January 1–15, 2001 at <a class="reference external" href="https://mail.python.org/pipermail/python-dev/2001-January/">https://mail.python.org/pipermail/python-dev/2001-January/</a>.</p>
|
||
</li>
|
||
<li><p>A new method, <code class="xref py py-meth docutils literal notranslate"><span class="pre">popitem()</span></code>, was added to dictionaries to enable
|
||
destructively iterating through the contents of a dictionary; this can be faster
|
||
for large dictionaries because there’s no need to construct a list containing
|
||
all the keys or values. <code class="docutils literal notranslate"><span class="pre">D.popitem()</span></code> removes a random <code class="docutils literal notranslate"><span class="pre">(key,</span> <span class="pre">value)</span></code> pair
|
||
from the dictionary <code class="docutils literal notranslate"><span class="pre">D</span></code> and returns it as a 2-tuple. This was implemented
|
||
mostly by Tim Peters and Guido van Rossum, after a suggestion and preliminary
|
||
patch by Moshe Zadka.</p></li>
|
||
<li><p>Modules can now control which names are imported when <code class="docutils literal notranslate"><span class="pre">from</span> <span class="pre">module</span> <span class="pre">import</span> <span class="pre">*</span></code>
|
||
is used, by defining an <code class="docutils literal notranslate"><span class="pre">__all__</span></code> attribute containing a list of names that
|
||
will be imported. One common complaint is that if the module imports other
|
||
modules such as <a class="reference internal" href="../library/sys.html#module-sys" title="sys: Access system-specific parameters and functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sys</span></code></a> or <a class="reference internal" href="../library/string.html#module-string" title="string: Common string operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">string</span></code></a>, <code class="docutils literal notranslate"><span class="pre">from</span> <span class="pre">module</span> <span class="pre">import</span> <span class="pre">*</span></code> will add
|
||
them to the importing module’s namespace. To fix this, simply list the public
|
||
names in <code class="docutils literal notranslate"><span class="pre">__all__</span></code>:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># List public names</span>
|
||
<span class="n">__all__</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'Database'</span><span class="p">,</span> <span class="s1">'open'</span><span class="p">]</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>A stricter version of this patch was first suggested and implemented by Ben
|
||
Wolfson, but after some python-dev discussion, a weaker final version was
|
||
checked in.</p>
|
||
</li>
|
||
<li><p>Applying <a class="reference internal" href="../library/functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code></a> to strings previously used octal escapes for
|
||
non-printable characters; for example, a newline was <code class="docutils literal notranslate"><span class="pre">'\012'</span></code>. This was a
|
||
vestigial trace of Python’s C ancestry, but today octal is of very little
|
||
practical use. Ka-Ping Yee suggested using hex escapes instead of octal ones,
|
||
and using the <code class="docutils literal notranslate"><span class="pre">\n</span></code>, <code class="docutils literal notranslate"><span class="pre">\t</span></code>, <code class="docutils literal notranslate"><span class="pre">\r</span></code> escapes for the appropriate characters,
|
||
and implemented this new formatting.</p></li>
|
||
<li><p>Syntax errors detected at compile-time can now raise exceptions containing the
|
||
filename and line number of the error, a pleasant side effect of the compiler
|
||
reorganization done by Jeremy Hylton.</p></li>
|
||
<li><p>C extensions which import other modules have been changed to use
|
||
<code class="xref py py-func docutils literal notranslate"><span class="pre">PyImport_ImportModule()</span></code>, which means that they will use any import hooks
|
||
that have been installed. This is also encouraged for third-party extensions
|
||
that need to import some other module from C code.</p></li>
|
||
<li><p>The size of the Unicode character database was shrunk by another 340K thanks
|
||
to Fredrik Lundh.</p></li>
|
||
<li><p>Some new ports were contributed: MacOS X (by Steven Majewski), Cygwin (by
|
||
Jason Tishler); RISCOS (by Dietmar Schwertberger); Unixware 7 (by Billy G.
|
||
Allie).</p></li>
|
||
</ul>
|
||
<p>And there’s the usual list of minor bugfixes, minor memory leaks, docstring
|
||
edits, and other tweaks, too lengthy to be worth itemizing; see the CVS logs for
|
||
the full details if you want them.</p>
|
||
</div>
|
||
<div class="section" id="acknowledgements">
|
||
<h2>Acknowledgements<a class="headerlink" href="#acknowledgements" title="Permalink to this headline">¶</a></h2>
|
||
<p>The author would like to thank the following people for offering suggestions on
|
||
various drafts of this article: Graeme Cross, David Goodger, Jay Graves, Michael
|
||
Hudson, Marc-André Lemburg, Fredrik Lundh, Neil Schemenauer, Thomas Wouters.</p>
|
||
</div>
|
||
</div>
|
||
|
||
|
||
</div>
|
||
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|
||
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|
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<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
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||
<div class="sphinxsidebarwrapper">
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||
<h3><a href="../contents.html">Table of Contents</a></h3>
|
||
<ul>
|
||
<li><a class="reference internal" href="#">What’s New in Python 2.1</a><ul>
|
||
<li><a class="reference internal" href="#introduction">Introduction</a></li>
|
||
<li><a class="reference internal" href="#pep-227-nested-scopes">PEP 227: Nested Scopes</a></li>
|
||
<li><a class="reference internal" href="#pep-236-future-directives">PEP 236: __future__ Directives</a></li>
|
||
<li><a class="reference internal" href="#pep-207-rich-comparisons">PEP 207: Rich Comparisons</a></li>
|
||
<li><a class="reference internal" href="#pep-230-warning-framework">PEP 230: Warning Framework</a></li>
|
||
<li><a class="reference internal" href="#pep-229-new-build-system">PEP 229: New Build System</a></li>
|
||
<li><a class="reference internal" href="#pep-205-weak-references">PEP 205: Weak References</a></li>
|
||
<li><a class="reference internal" href="#pep-232-function-attributes">PEP 232: Function Attributes</a></li>
|
||
<li><a class="reference internal" href="#pep-235-importing-modules-on-case-insensitive-platforms">PEP 235: Importing Modules on Case-Insensitive Platforms</a></li>
|
||
<li><a class="reference internal" href="#pep-217-interactive-display-hook">PEP 217: Interactive Display Hook</a></li>
|
||
<li><a class="reference internal" href="#pep-208-new-coercion-model">PEP 208: New Coercion Model</a></li>
|
||
<li><a class="reference internal" href="#pep-241-metadata-in-python-packages">PEP 241: Metadata in Python Packages</a></li>
|
||
<li><a class="reference internal" href="#new-and-improved-modules">New and Improved Modules</a></li>
|
||
<li><a class="reference internal" href="#other-changes-and-fixes">Other Changes and Fixes</a></li>
|
||
<li><a class="reference internal" href="#acknowledgements">Acknowledgements</a></li>
|
||
</ul>
|
||
</li>
|
||
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|
||
|
||
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|
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