alex23 wrote:
On Oct 30, 1:10 pm, Nick Stinemates <n...@stinemates.org> wrote:
Some objects are singletons, ie there's only ever one of them. The most
common singleton is None. In virtually every other case you should be
using "==" and "!=".
Please correct me if I am wrong, but I believe you meant to say some
objects are immutable, in which case you would be correct.
You're completely wrong. Immutability has nothing to do with identity,
which is what 'is' is testing for:
What immutability has to do with identity is that 'two' immutable
objects with the same value *may* actually be the same object,
*depending on the particular version of a particular implementation*.
t1 = (1,2,3) # an immutable object
t2 = (1,2,3) # another immutable object
Whether or not this is 'another' object or the same object is irrelevant
for all purposes except identity checking. It is completely up to the
interpreter.
t1 is t2
False
In this case, but it could have been True.
t1 == t2
True
MRAB was refering to the singleton pattern[1], of which None is the
predominant example in Python. None is _always_ None, as it's always
the same object.
And in 3.x, the same is true of True and False.
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