But if I chose as a value another number (a big one, let say 1e10) I
get what I will expect also in the case of the chose of the integer 10
showed above:
a=1e10
d=1e10
d is a
False
id(a)
11388984
id(d)
11388920
CPython has the option to cache frequently used items, and does
so for a small range of ints. It's not guaranteed behavior (or a
guaranteed range) so you shouldn't rely on it, but it's an
efficiency thing. In my current version, it looks like it's ints
from -5 to 256. YMMV
In general, if you're using "is" (and not comparing with None) or
id(), you're doing it wrong unless you already know the
peculiarities of Python's identity implementations.
-tkc
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