Unsupported operand type(s) for *: 'NoneType' and 'NoneType'

Unsupported operand type(s) for *: 'NoneType' and 'NoneType' #

The Python "TypeError: unsupported operand type(s) for *: 'NoneType' and 'NoneType'" occurs when we try to use the multiplication operator with None values. To solve the error, figure out where the variables got assigned a None value and correct the assignment.

Here is an example of how the error occurs.

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my_value_1 = None

my_value_2 = None

# ⛔️ TypeError: unsupported operand type(s) for *: 'NoneType' and 'NoneType'
result = my_value_1 * my_value_2

The variables we are trying to multiply store a None value which caused the error.

We can't use the multiplication operator with a None value on either side.

The most common sources of None values are:

1. Having a function that doesn't return anything (returns None implicitly).
2. Explicitly setting a variable to None.
3. Assigning a variable to the result of calling a built-in function that doesn't return anything.
4. Having a function that only returns a value if a certain condition is met.

Make sure you aren't calling a function that doesn't return anything and expecting the return value to be a number.

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# 👇️ this function returns None
def get_num():
    print(10)


# ⛔️ TypeError: unsupported operand type(s) for *: 'NoneType' and 'NoneType'
result = get_num() * get_num()

The get_num function doesn't return anything, therefore it implicitly returns None.

You can use a return statement to return a value from a function.

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def get_num():
    return 10

result = get_num() * get_num()

print(result)  # 👉️ 100

Use an if statement if you need to check whether a variable doesn't store a None value before using the multiplication (*) operator.

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my_num_1 = None

my_num_2 = 15

if my_num_1 is not None:
    result = my_num_1 * my_num_2
    print(result)
else:
    # 👇️ this runs
    print('variable stores a None value')

Alternatively, you can provide a default value if the variable stores None.

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my_num_1 = None

my_num_2 = 15

if my_num_1 is None:
    my_num_1 = 2

result = my_num_1 * my_num_2

print(result)  # 👉️ 30

We check if the my_num_1 variable stores a None value and if it does, we set it to 2.

Make sure you aren't storing the result of calling one in a variable.

Another common cause of the error is having a function that returns a value only if a condition is met.

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def get_num(a):
    if a > 15:
        return a


my_num_1 = get_num(10)
print(my_num_1)  # 👉️ None

my_num_2 = get_num(14)
print(my_num_2)  # 👉️ None


# ⛔️ TypeError: unsupported operand type(s) for *: 'NoneType' and 'NoneType'
result = my_num_1 * my_num_2

The if block in the get_num function is only run if the passed in number is greater than 15.

To solve the error in this scenario, you either have to check if the function didn't return None or return a default value if the condition is not met.

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def get_num(a):
    if a > 15:
        return a

    return 2  # 👈️ return fallback if condition not met


my_num_1 = get_num(10)

my_num_2 = get_num(14)


result = my_num_1 * my_num_2
print(result)  # 👉️ 4

Now the function is guaranteed to return a value regardless if the condition is met.

Conclusion #

The Python "TypeError: unsupported operand type(s) for *: 'NoneType' and 'NoneType'" occurs when we try to use the multiplication operator with None values. To solve the error, figure out where the variables got assigned a None value and correct the assignment.