On 3 November 2012 22:50, Chris Angelico <ros...@gmail.com> wrote: > This one I haven't checked the source for, but ISTR discussions on > this list about comparison of two unequal interned strings not being > optimized, so they'll end up being compared char-for-char. Using 'is' > guarantees that the check stops with identity. This may or may not be > significant, and as you say, defending against an uninterned string > slipping through is potentially critical.
The source is here (and it shows what you suggest): http://hg.python.org/cpython/file/6c639a1ff53d/Objects/unicodeobject.c#l6128 Comparing strings char for char is really not that big a deal though. This has been discussed before: you don't need to compare very many characters to conclude that strings are unequal (if I remember correctly you were part of that discussion). I can imagine cases where I might consider using intern on lots of strings to speed up comparisons but I would have to be involved in some seriously heavy and obscure string processing problem before I considered using 'is' to compare those interned strings. That is confusing to anyone who reads the code, prone to bugs and unlikely to achieve the desired outcome of speeding things up (noticeably). Oscar -- http://mail.python.org/mailman/listinfo/python-list
