Check if current thread is main thread, in Python

Question

This has been answered for Android, Objective C and C++ before, but apparently not for Python. How do I reliably determine whether the current thread is the main thread? I c

Answer 1

The problem with threading.current_thread().name == 'MainThread' is that one can always do:

threading.current_thread().name = 'MyName'
assert threading.current_thread().name == 'MainThread' # will fail

Perhaps the following is more solid:

threading.current_thread().__class__.__name__ == '_MainThread'

Having said that, one may still cunningly do:

threading.current_thread().__class__.__name__ = 'Grrrr'
assert threading.current_thread().__class__.__name__ == '_MainThread' # will fail

But this option still seems better; "after all, we're all consenting adults here."

UPDATE:

Python 3.4 introduced threading.main_thread() which is much better than the above:

assert threading.current_thread() is threading.main_thread()

UPDATE 2:

For Python < 3.4, perhaps the best option is:

isinstance(threading.current_thread(), threading._MainThread)

Answer 2

The answers here are old and/or bad, so here's a current solution:

if threading.current_thread() is threading.main_thread():
    ...

This method is available since Python 3.4+.

Answer 3

If, like me, accessing protected attributes gives you the Heebie-jeebies, you may want an alternative for using threading._MainThread, as suggested. In that case, you may exploit the fact that only the Main Thread can handle signals, so the following can do the job:

import signal
def is_main_thread():
    try:
        # Backup the current signal handler
        back_up = signal.signal(signal.SIGINT, signal.SIG_DFL)
    except ValueError:
        # Only Main Thread can handle signals
        return False
    # Restore signal handler
    signal.signal(signal.SIGINT, back_up)
    return True

Updated to address potential issue as pointed out by @user4815162342.