Test for object identity should be is¶
Testing the identity of two objects can be achieved in python with a special operator called is.
Most prominently it is used to check whether a variable points to None.
But the operator can examine any kind of identity.
This often leads to confusion because equality of two different objects will return False.
Anti-pattern¶
a = range(10)
b = range(10)
print((a is b))
This code snippet will print False even though a and b have equal values.
This can occur because a and b are references that point to different objects which happen to have the same value.
To verify the equality of two variables the == operator should be used.
Best practice¶
Only use the is operator if you want to check the exact identity of two references.
some_list = None
if some_list is None:
do_somthing_with_the_list()