pythonpython-3.xoperatorsequality

What is the difference between "not ==" and "!="?

I was looking at google, but I could not find an answer.

if 5 != 10:
    print('True')

# True

if not 5 == 10:
    print('True')

# True

Both seem to do the same. When to use "not ==" and when to use "!="?

Solution

  • In the case of a comparison with two integers, they are the same. Prefer != as more pythonic.

    The result may differ if either operand is an instance of a custom class. Custom classes are free to override == and != operator independently (even with insane results)

    From the LHS:

    >>> class A:
...     def __eq__(self, other):
...         return False
...     def __ne__(self, other):
...         return False
...     
>>> a = A()
>>> a != 5
False
>>> not a == 5
True

    From the RHS:

    >>> class R(str):
...     def __eq__(self, other):
...         return False
...     def __ne__(self, other):
...         return False
...     
>>> r = R()
>>> 'spam' != r
False
>>> not 'spam' == r
True