On Sat, Feb 22, 2014 at 4:01 PM, Steven D'Aprano <[email protected]> wrote: > (Chris, I think that ought to go in the motivation section of the PEP.)
Added to my draft, and here's the peps diff: diff -r c52a2ae3d98e pep-0463.txt --- a/pep-0463.txt Fri Feb 21 23:27:51 2014 -0500 +++ b/pep-0463.txt Sat Feb 22 16:33:37 2014 +1100 @@ -43,6 +43,34 @@ * statistics.mean(data) - no way to handle an empty iterator +Had this facility existed early in Python's history, there would have been +no need to create dict.get() and related methods; the one obvious way to +handle an absent key would be to respond to the exception. One method is +written which signal the absence in one way, and one consistent technique +is used to respond to the absence. Instead, we have dict.get(), and as of +Python 3.4, we also have min(... default=default), and myriad others. We +have a LBYL syntax for testing inside an expression, but there is currently +no EAFP notation; compare the following:: + + # LBYL: + if key in dic: + process(dic[key]) + else: + process(None) + # As an expression: + process(dic[key] if key in dic else None) + + # EAFP: + try: + process(dic[key]) + except KeyError: + process(None) + # As an expression: + process(dic[key] except KeyError: None) + +Python generally recommends the EAFP policy, but must then proliferate +utility functions like dic.get(key,None) to enable this. + Rationale ========= _______________________________________________ Python-Dev mailing list [email protected] https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com