Python 'is not' operator
Question:
I notice there is a comparison operator is not. Should I literally translate it into
!=
instead of
== not
?
Answers:
A != B
means that “A is not equal to B”, not “A is equal to not B”.
It’s not a relational comparison; it’s identity. And it translates to not (A is B).
To expand on what Ignacio said:
a == b and a != b test whether two objects have the same value. You can override an object’s __eq__ and __ne__ methods to determine what that means.
a is b and a is not b test whether two objects are the same thing. It’s like doing id(a) == id(b).
Python 2.7.3 documentation, 5.9. Comparisons:
The operators <, >, ==, >=, <=, and != compare the values of two objects.
and about operator is in the same chapter:
The operators is and is not test for object identity: x is y is true if and only if x and y are the same object. x is not y yields the inverse truth value.
I notice there is a comparison operator is not. Should I literally translate it into
!=
instead of
== not
?
A != B
means that “A is not equal to B”, not “A is equal to not B”.
It’s not a relational comparison; it’s identity. And it translates to not (A is B).
To expand on what Ignacio said:
a == b and a != b test whether two objects have the same value. You can override an object’s __eq__ and __ne__ methods to determine what that means.
a is b and a is not b test whether two objects are the same thing. It’s like doing id(a) == id(b).
Python 2.7.3 documentation, 5.9. Comparisons:
The operators <, >, ==, >=, <=, and != compare the values of two objects.
and about operator is in the same chapter:
The operators is and is not test for object identity: x is y is true if and only if x and y are the same object. x is not y yields the inverse truth value.