What Is the "None" Keyword in Python?

In Python, None is a built-in constant that implies absence of value (or a null value):

For example, you can assign None to a variable in the following way:

foo = None
print(foo) # None

Similarly, you can assign None to a function/method argument (to serve as a default value), like so:

def foo(param = None):
    if param is None:
        return 'empty'

print(foo()) # 'empty'

None can also be returned from a function:

def foo():
    return None

print(foo()) # None

When a function/method does not explicitly return a value, it is implicitly None:

def foo():

print(foo()) # None

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