Python 3: Catching warnings during multiprocessing

Question

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The warnings.catch_warnings() context manager is not thread safe. How do I use it in a parallel processing environment?

Background<

Answer 1

you can try to override the Process.run method to use warnings.catch_warnings.

>>> from multiprocessing import Process
>>> 
>>> def yell(text):
...    import warnings
...    print 'about to yell %s' % text
...    warnings.warn(text)
... 
>>> class CustomProcess(Process):
...    def run(self, *args, **kwargs):
...       import warnings
...       with warnings.catch_warnings():
...          warnings.simplefilter("ignore")
...          return Process.run(self, *args, **kwargs)
... 
>>> if __name__ == '__main__':
...    quiet = CustomProcess(target=yell, args=('...not!',))
...    quiet.start()
...    quiet.join()
...    noisy = Process(target=yell, args=('AAAAAAaaa!',))
...    noisy.start()
...    noisy.join()
... 
about to yell ...not!
about to yell AAAAAAaaa!
__main__:4: UserWarning: AAAAAAaaa!
>>> 

or you can use some of the internals... (__warningregistry__)

>>> from multiprocessing import Process
>>> import exceptions
>>> def yell(text):
...    import warnings
...    print 'about to yell %s' % text
...    warnings.warn(text)
...    # not filtered
...    warnings.warn('complimentary second warning.')
... 
>>> WARNING_TEXT = 'AAAAaaaaa!'
>>> WARNING_TYPE = exceptions.UserWarning
>>> WARNING_LINE = 4
>>> 
>>> class SelectiveProcess(Process):
...    def run(self, *args, **kwargs):
...       registry = globals().setdefault('__warningregistry__', {})
...       registry[(WARNING_TEXT, WARNING_TYPE, WARNING_LINE)] = True
...       return Process.run(self, *args, **kwargs)
... 
>>> if __name__ == '__main__':
...    p = SelectiveProcess(target=yell, args=(WARNING_TEXT,))
...    p.start()
...    p.join()
... 
about to yell AAAAaaaaa!
__main__:6: UserWarning: complimentary second warning.
>>>