"Is None" vs. "== None": A Beginner's Guide to Python Identity and Equality

Identity (is):

• foo is None checks if the object foo is the exact same object as the special value None.
• Think of it like asking "are these two pointers pointing to the same memory location?"
• This is useful when you're working with specific objects and want to compare their identity, not just their value.

Equality (==):

• foo == None checks if the value of foo is equal to the value of None.
• It's like asking "do these two values represent the same thing?"
• This is more commonly used for general value comparisons, regardless of the object itself.

Singularity of None:

• There's only one None object in Python. So, comparing None with itself using is will always be True.
• But, comparing other objects with None using is might not be what you expect.

Custom comparison:

• While None has a default __eq__ method, other objects can define their own comparison logic.
• This means foo == None might not always return True even if foo is None.

Simple case:

x = None
y = None

print(x is None)  # True
print(x == None)  # True (both check for None value)

z = 0
print(z is None)  # False (different objects)
print(z == None)  # False (different values)

Custom comparison:

class CustomObject:
  def __eq__(self, other):
    return other is None  # Always equal to None

obj = CustomObject()

print(obj is None)  # False (different objects)
print(obj == None)  # True (custom logic)

• Use foo is None when you want to check if foo is the exact same object as None.
• Use foo == None when you want to check if the value of foo is equal to the value of None.
• Be aware that custom object comparisons might affect == behavior.

I hope this explanation clarifies the difference between is and == with None in Python!