On Tue, 04 Mar 2014 00:22:55 +0200, Marko Rauhamaa wrote: > Jerry Hill <malaclyp...@gmail.com>: > >> except for the fact that there has been 20 years of custom saying that >> comparing to None with equality is wrong. > > "if foo == None" is not wrong in any manner. It's just that if you are > comfortable with the "is" operator and its semantics, "if foo is None" > is slightly more natural. > > You generally use "==" if more than one object could be equal. If you > know there's only one object of the kind, you convey that knowledge by > the use of "is" even when functionally, it doesn't matter.
I don't agree that it doesn't matter. Code, even when functionally equivalent, should express the intention of the programmer in as simple a fashion as is possible given the constraints of the task, performance, etc. For example, if you want to add 1 to a number, you would write: x += 1 not: x += (127 - 102)//(5**2) even though you know that the two expressions are exactly equivalent. Even if you know that there is a peep-hole optimizer that ensures that the code actually compiled is "x += 1". The intention to the reader is important. This is why, unless performance is *really* critical, one should normally write x*2 when multiplying x by 2 rather than x >> 1. (And in Python, the overhead means that there is no real performance benefit to using bit shifts instead of multiplication or division.) If your intention is to treat None as a singleton sentinel, not as a value, then you ought to use "is" to signal that intention, rather than using == even if you know that there won't be any false positives. -- Steven -- https://mail.python.org/mailman/listinfo/python-list
