__main__ — Top-level script environment

This module represents the (otherwise anonymous) scope in which the interpreter’s main program executes — commands read either from standard input, from a script file, or from an interactive prompt. It is this environment in which the idiomatic “conditional script” stanza causes a script to run:

if __name__ == "__main__":
    main()

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https://docs.python.org/2.7/library/__main__.html