Python None
Python None
None is a special constant in Python that represents the absence of a value.
Its data type is NoneType, and None is the only instance of a NoneType object.
NoneType
Variables can be assigned None to indicate "no value" or "not set".
Use type() to see the type of a None value.
Comparing to None
To compare a value to None, use the identity operator is or is not
Example
Use the identity operator is for comparisons with None:
result = None
if result is None:
print("No result yet")
else:
print("Result is ready")
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if result is None:
print("No result yet")
else:
print("Result is ready")
Example
Similar example, but using is not instead:
result = None
if result is not None:
print("Result is ready")
else:
print("No result yet")
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if result is not None:
print("Result is ready")
else:
print("No result yet")
True or False
None evaluates to False in a boolean context.
Functions returning None
Functions that do not explicitly return a value return None by default.
Example
A function without a return statement returns None:
def myfunc():
x = 5
x = myfunc()
print(x)
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x = 5
x = myfunc()
print(x)