This frequently-asked question appears, for example, in this Usenet posting. No single answer is canonical, for each has definite liabilities and limitations; there are, however, a number of expedients which apply in at least some situations:

• "fire and forget", that is, put the subprocess in the background and let it run freely;

• put the subprocess in the background, return to the GUI's event loop, and poll to detect when the subprocess has terminated;

• put the subprocess in its own thread, and rely on Python ThreadProgramming ...;

• launch subprocess.Popen() in a conventional way, but interleave attention in a single thread of control between the GUI controller and the stdout from the subprocess.

• the particular GUI framework involved--wxPython, TkInter, probably has specific mechanisms for managing concurrency in an event-based way. The toolkit behind Tkinter, in fact, already has a Wiki page on the subject above, many of whose hints can be adapted to other frameworks;

• ...

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