[Python-Dev] cpython: Rename contextlib.ignored() to contextlib.ignore(). (original) (raw)

Antoine Pitrou solipsis at pitrou.net
Wed Oct 16 14:24:11 CEST 2013

Le Wed, 16 Oct 2013 14:09:16 +0200, Antoine Pitrou <solipsis at pitrou.net> a écrit :

Le Wed, 16 Oct 2013 14:01:37 +0200, Victor Stinner <victor.stinner at gmail.com> a écrit : > 2013/10/16 Antoine Pitrou <solipsis at pitrou.net>: > >> By the way, what are the performances of contextlib.ignore()? > >> Exceptions can be slow in some cases. Adding something even > >> slower would not be a good idea. > > > > A "try" block which succeeds is fast. > > Ah yes, I never reminder this fact. I try to not care too much of > micro-optimizations :-)

It's not so much a micro-optimization than the fact that pushing a block on the stack is very cheap. IIRC, what is expensive is: - creating the exception object with the associated traceback - matching the exception in the "exception SomeException" clause

By the way, of course this must be kept in proportion. At worse the total cost is a couple of microseconds. Still, a simplistic micro-benchmark:

$ ./python -m timeit "try: pass" "except Exception: pass" 100000000 loops, best of 3: 0.0164 usec per loop

$ ./python -m timeit -s "from contextlib import ignore" "with ignore(Exception): pass" 100000 loops, best of 3: 2.21 usec per loop

Regards

Antoine.

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