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<div class="section" id="module-pty">
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<span id="pty-pseudo-terminal-utilities"></span><h1><a class="reference internal" href="#module-pty" title="pty: Pseudo-Terminal Handling for Linux. (Linux)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">pty</span></code></a> — Pseudo-terminal utilities<a class="headerlink" href="#module-pty" title="Permalink to this headline">¶</a></h1>
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<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/pty.py">Lib/pty.py</a></p>
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<hr class="docutils" />
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<p>The <a class="reference internal" href="#module-pty" title="pty: Pseudo-Terminal Handling for Linux. (Linux)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">pty</span></code></a> module defines operations for handling the pseudo-terminal
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concept: starting another process and being able to write to and read from its
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controlling terminal programmatically.</p>
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<p>Because pseudo-terminal handling is highly platform dependent, there is code to
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do it only for Linux. (The Linux code is supposed to work on other platforms,
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but hasn’t been tested yet.)</p>
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<p>The <a class="reference internal" href="#module-pty" title="pty: Pseudo-Terminal Handling for Linux. (Linux)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">pty</span></code></a> module defines the following functions:</p>
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<dl class="function">
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<dt id="pty.fork">
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<code class="descclassname">pty.</code><code class="descname">fork</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#pty.fork" title="Permalink to this definition">¶</a></dt>
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<dd><p>Fork. Connect the child’s controlling terminal to a pseudo-terminal. Return
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value is <code class="docutils literal notranslate"><span class="pre">(pid,</span> <span class="pre">fd)</span></code>. Note that the child gets <em>pid</em> 0, and the <em>fd</em> is
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<em>invalid</em>. The parent’s return value is the <em>pid</em> of the child, and <em>fd</em> is a
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file descriptor connected to the child’s controlling terminal (and also to the
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child’s standard input and output).</p>
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</dd></dl>
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<dl class="function">
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<dt id="pty.openpty">
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<code class="descclassname">pty.</code><code class="descname">openpty</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#pty.openpty" title="Permalink to this definition">¶</a></dt>
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<dd><p>Open a new pseudo-terminal pair, using <a class="reference internal" href="os.html#os.openpty" title="os.openpty"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.openpty()</span></code></a> if possible, or
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emulation code for generic Unix systems. Return a pair of file descriptors
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<code class="docutils literal notranslate"><span class="pre">(master,</span> <span class="pre">slave)</span></code>, for the master and the slave end, respectively.</p>
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</dd></dl>
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<dl class="function">
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<dt id="pty.spawn">
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<code class="descclassname">pty.</code><code class="descname">spawn</code><span class="sig-paren">(</span><em>argv</em><span class="optional">[</span>, <em>master_read</em><span class="optional">[</span>, <em>stdin_read</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#pty.spawn" title="Permalink to this definition">¶</a></dt>
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<dd><p>Spawn a process, and connect its controlling terminal with the current
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process’s standard io. This is often used to baffle programs which insist on
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reading from the controlling terminal. It is expected that the process
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spawned behind the pty will eventually terminate, and when it does <em>spawn</em>
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will return.</p>
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<p>The functions <em>master_read</em> and <em>stdin_read</em> are passed a file descriptor
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which they should read from, and they should always return a byte string. In
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order to force spawn to return before the child process exits an
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<a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a> should be thrown.</p>
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<p>The default implementation for both functions will read and return up to 1024
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bytes each time the function is called. The <em>master_read</em> callback is passed
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the pseudoterminal’s master file descriptor to read output from the child
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process, and <em>stdin_read</em> is passed file descriptor 0, to read from the
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parent process’s standard input.</p>
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<p>Returning an empty byte string from either callback is interpreted as an
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end-of-file (EOF) condition, and that callback will not be called after
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that. If <em>stdin_read</em> signals EOF the controlling terminal can no longer
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communicate with the parent process OR the child process. Unless the child
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process will quit without any input, <em>spawn</em> will then loop forever. If
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<em>master_read</em> signals EOF the same behavior results (on linux at least).</p>
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<p>If both callbacks signal EOF then <em>spawn</em> will probably never return, unless
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<em>select</em> throws an error on your platform when passed three empty lists. This
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is a bug, documented in <a class="reference external" href="https://bugs.python.org/issue26228">issue 26228</a>.</p>
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<div class="versionchanged">
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<p><span class="versionmodified changed">Changed in version 3.4: </span><a class="reference internal" href="#pty.spawn" title="pty.spawn"><code class="xref py py-func docutils literal notranslate"><span class="pre">spawn()</span></code></a> now returns the status value from <a class="reference internal" href="os.html#os.waitpid" title="os.waitpid"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.waitpid()</span></code></a>
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on the child process.</p>
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</div>
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</dd></dl>
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<div class="section" id="example">
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<h2>Example<a class="headerlink" href="#example" title="Permalink to this headline">¶</a></h2>
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<p>The following program acts like the Unix command <em class="manpage">script(1)</em>, using a
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pseudo-terminal to record all input and output of a terminal session in a
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“typescript”.</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">argparse</span>
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<span class="kn">import</span> <span class="nn">os</span>
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<span class="kn">import</span> <span class="nn">pty</span>
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<span class="kn">import</span> <span class="nn">sys</span>
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<span class="kn">import</span> <span class="nn">time</span>
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<span class="n">parser</span> <span class="o">=</span> <span class="n">argparse</span><span class="o">.</span><span class="n">ArgumentParser</span><span class="p">()</span>
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<span class="n">parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span><span class="s1">'-a'</span><span class="p">,</span> <span class="n">dest</span><span class="o">=</span><span class="s1">'append'</span><span class="p">,</span> <span class="n">action</span><span class="o">=</span><span class="s1">'store_true'</span><span class="p">)</span>
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<span class="n">parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span><span class="s1">'-p'</span><span class="p">,</span> <span class="n">dest</span><span class="o">=</span><span class="s1">'use_python'</span><span class="p">,</span> <span class="n">action</span><span class="o">=</span><span class="s1">'store_true'</span><span class="p">)</span>
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<span class="n">parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span><span class="s1">'filename'</span><span class="p">,</span> <span class="n">nargs</span><span class="o">=</span><span class="s1">'?'</span><span class="p">,</span> <span class="n">default</span><span class="o">=</span><span class="s1">'typescript'</span><span class="p">)</span>
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<span class="n">options</span> <span class="o">=</span> <span class="n">parser</span><span class="o">.</span><span class="n">parse_args</span><span class="p">()</span>
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<span class="n">shell</span> <span class="o">=</span> <span class="n">sys</span><span class="o">.</span><span class="n">executable</span> <span class="k">if</span> <span class="n">options</span><span class="o">.</span><span class="n">use_python</span> <span class="k">else</span> <span class="n">os</span><span class="o">.</span><span class="n">environ</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s1">'SHELL'</span><span class="p">,</span> <span class="s1">'sh'</span><span class="p">)</span>
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<span class="n">filename</span> <span class="o">=</span> <span class="n">options</span><span class="o">.</span><span class="n">filename</span>
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<span class="n">mode</span> <span class="o">=</span> <span class="s1">'ab'</span> <span class="k">if</span> <span class="n">options</span><span class="o">.</span><span class="n">append</span> <span class="k">else</span> <span class="s1">'wb'</span>
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<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="n">filename</span><span class="p">,</span> <span class="n">mode</span><span class="p">)</span> <span class="k">as</span> <span class="n">script</span><span class="p">:</span>
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<span class="k">def</span> <span class="nf">read</span><span class="p">(</span><span class="n">fd</span><span class="p">):</span>
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<span class="n">data</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">read</span><span class="p">(</span><span class="n">fd</span><span class="p">,</span> <span class="mi">1024</span><span class="p">)</span>
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<span class="n">script</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
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<span class="k">return</span> <span class="n">data</span>
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<span class="nb">print</span><span class="p">(</span><span class="s1">'Script started, file is'</span><span class="p">,</span> <span class="n">filename</span><span class="p">)</span>
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<span class="n">script</span><span class="o">.</span><span class="n">write</span><span class="p">((</span><span class="s1">'Script started on </span><span class="si">%s</span><span class="se">\n</span><span class="s1">'</span> <span class="o">%</span> <span class="n">time</span><span class="o">.</span><span class="n">asctime</span><span class="p">())</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>
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<span class="n">pty</span><span class="o">.</span><span class="n">spawn</span><span class="p">(</span><span class="n">shell</span><span class="p">,</span> <span class="n">read</span><span class="p">)</span>
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<span class="n">script</span><span class="o">.</span><span class="n">write</span><span class="p">((</span><span class="s1">'Script done on </span><span class="si">%s</span><span class="se">\n</span><span class="s1">'</span> <span class="o">%</span> <span class="n">time</span><span class="o">.</span><span class="n">asctime</span><span class="p">())</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>
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<span class="nb">print</span><span class="p">(</span><span class="s1">'Script done, file is'</span><span class="p">,</span> <span class="n">filename</span><span class="p">)</span>
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</pre></div>
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<ul>
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<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">pty</span></code> — Pseudo-terminal utilities</a><ul>
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<li><a class="reference internal" href="#example">Example</a></li>
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<p class="topless"><a href="tty.html"
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title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">tty</span></code> — Terminal control functions</a></p>
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<p class="topless"><a href="fcntl.html"
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title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">fcntl</span></code> — The <code class="docutils literal notranslate"><span class="pre">fcntl</span></code> and <code class="docutils literal notranslate"><span class="pre">ioctl</span></code> system calls</a></p>
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