On 4/20/2012 9:34 PM, john.tant...@gmail.com wrote:
On Friday, April 20, 2012 12:34:46 PM UTC-7, Rotwang wrote:
I believe it says somewhere in the Python docs that it's undefined and
implementation-dependent whether two identical expressions have the same
identity when the result of each is immutable
Bad design. Where "is" is ill-defined, it should raise ValueError.
A worse example, one which is very implementation-dependent:
http://stackoverflow.com/questions/306313/python-is-operator-behaves-unexpectedly-with-integers
>>> a = 256
>>> b = 256
>>> a is b
True # this is an expected result
>>> a = 257
>>> b = 257
>>> a is b
False
Operator "is" should be be an error between immutables
unless one is a built-in constant. ("True" and "False"
should be made hard constants, like "None". You can't assign
to None, but you can assign to True, usually with
unwanted results. It's not clear why True and False
weren't locked down when None was.)
John Nagle
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