Mike Pomraning mjp at pilcrow.madison.wi.us
Wed Dec 17 12:12:57 EST 2014

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It strikes me as oddly dangerous that signal.signal() accepts callable handlers of the wrong arity:

    def timeout_cleanup():
      ...

    signal.signal(signal.SIGALRM, timeout_cleanup)       # I desire a TypeError here
    signal.alarm(PROCESS_TIMEOUT)

    ... time passes ...

    TypeError: timeout_cleanup() takes 0 positional arguments but 2 were given

(Similar TypeError with different text under python 2.)

The downside to current behavior is that the coding error is revealed only under certain conditions at runtime.  In the example above, you don't know that your seatbelt is defective until you need it.

Does anyone disagree with modifying signal.signal's behavior to raise a TypeError when given a user-defined handler of the wrong arity?  Any code relying on this behavior is, IMO, contrived beyond plausibility.  However, this change might break code not yet known to be incorrect.

If no disagreements, patch or PEP?

-Mike

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