Roger Miller wrote: > Steve R. Hastings wrote: > > >>a = 0 >>b = 0 >>a is b # always true > > > Is this guaranteed by the Python specification, or is it an artifact of > the current implementation?
AFAIK it's an artifact. The performance hit it Python stopped sharing small integers could be enormous, nonetheless sharing isn't part of the specification > My understanding has been that an > implementation is free to share integer objects or not, so using 'is' > as an equality test takes you into undefined territory, regardless of > the size of the value. > I agree. "is" is for working with linked-lists or trees, or other applications where object identity is really and truly what you're interested in. Some amusing is/== facts, some suggested by recent threads Python 2.4.2 (#1, Jan 23 2006, 21:24:54) [GCC 3.3.4] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> 0 is 0.0 False >>> -0.0 is 0.0 False >>> 0 == 0.0 == -0.0 True >>> 1000000 is (2000000/2) False -- http://mail.python.org/mailman/listinfo/python-list
