In simple terms, why this code returns False and not true:
a = 10
print(id(a) is id(a)) # why false?
id() returns integer, and same integer vars point to the same integer object. Why it returns false then? What is the difference with:
a = 10
b = 10
print(a is b) # it returns True
Thanks for explanation.
Because, while it is true that
a is a
id(a) is a large integer and does not compare by is
>>> a = 10
>>> print(id(a) is id(a))
False
>>> print(id(a),id(a))
(44337068, 44337068)
>>>
Check https://docs.python.org/2/c-api/int.html#c.PyInt_FromLong for which integers compare by is - but remember that is an implementation detail so don't rely on it (always compare ints with ==):
>>> a = 256
>>> b = 256
>>> a is b
True
>>> a = 257
>>> b = 257
>>> a is b
False
(from "is" operator behaves unexpectedly with integers)
For further motivation to always use ==, the following:
a = 300
b = 300
print(a is b)
print(a is 300)
def c(a): return a is 300
def d(a): return a is b
print(c(a))
print(d(a))
when saved to a file and run, prints True, True, False, and True...