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python-3.7.4-docs-html/_sources/library/__main__.rst.txt

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+:mod:`__main__` --- Top-level script environment
+================================================
+
+.. module:: __main__
+   :synopsis: The environment where the top-level script is run.
+
+--------------
+
+``'__main__'`` is the name of the scope in which top-level code executes.
+A module's __name__ is set equal to ``'__main__'`` when read from
+standard input, a script, or from an interactive prompt.
+
+A module can discover whether or not it is running in the main scope by
+checking its own ``__name__``, which allows a common idiom for conditionally
+executing code in a module when it is run as a script or with ``python
+-m`` but not when it is imported::
+
+   if __name__ == "__main__":
+       # execute only if run as a script
+       main()
+
+For a package, the same effect can be achieved by including a
+``__main__.py`` module, the contents of which will be executed when the
+module is run with ``-m``.