Does '!=' equivelent to 'is not'
johnjsal at gmailNOSPAM.com
Tue Jun 17 05:51:24 CEST 2008
John Salerno wrote:
> == and != test to see if the *value* of
> two variables are the same.
Let me just clarify this. It might seem like a picky point, but I think
it's pretty important when learning Python.
I don't really mean the value of the variables themselves, I mean the
values that the variables refer to. The variables themselves aren't
actually the objects, nor do they have values, exactly. Instead, they
*refer* to objects in memory, and it is these objects that we are
testing the values and identities of. For example, using that previous code:
a ---> 'hello world'
b ---> 'hello world'
---> 'hello world'
a and b were assigned to two separate objects (it doesn't matter that
they happen to be the same value). As you can see above, a and b refer
to different things.
c and d, however, were assigned simultaneously to the same object, and
therefore refer to a single object in memory. This is why "c is d" is
True, but "a is b" is False.
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