'<' not supported between instances of 'NoneType' and 'int'

'<' not supported between instances of 'NoneType' and 'int' #

The Python "TypeError: '<' not supported between instances of 'NoneType' and 'int'" occurs when we use a comparison operator between a None value and a int. To solve the error, figure out where the None value comes from and correct the assignment.

Here is an example of how the error occurs.

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my_int_1 = None

my_int_2 = 10

# ⛔️ TypeError: '<' not supported between instances of 'NoneType' and 'int'
if my_int_1 < my_int_2:
    print('success')

We used a comparison operator between values of incompatible types (None and int) which caused the error.

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 certain condition is met.

Functions that don't explicitly return a value return None.

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# 👇️ this function returns None
def get_int():
    print(20)


my_int_2 = 10

# ⛔️ TypeError: '>' not supported between instances of 'NoneType' and 'int'
if get_int() > my_int_2:
    print('success')

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

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def get_int():
    return 20


my_int_2 = 10

if get_int() > my_int_2:
    # ✅ this runs
    print('success')

Use an if statement if you need to check whether a variable doesn't store a None value before using a comparison operator.

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my_int_1 = None

my_int_2 = 10

if my_int_1 is not None:
    print(my_int_1 < my_int_2)
else:
    # 👉️ this runs
    print('Variable stores a None value')

Alternatively, you can set the variable to 0 if it stores None.

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my_int_1 = None

my_int_2 = 10

if my_int_1 is None:
    my_int_1 = 0

print(my_int_1 < my_int_2)  # 👉️ True

If the my_int_1 variable stores a None value, we set it to 0 before using a comparison operator.

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_int(a):
    if a > 5:
        return a


my_int_1 = get_int(4)
print(my_int_1)  # 👉️ None

my_int_2 = 10

# ⛔️ TypeError: '>' not supported between instances of 'NoneType' and 'int'
print(my_int_1 > my_int_2)

The if statement in the get_int function is only ran if the passed in number is greater than 5.

To solve the error, 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_int(a):
    if a > 5:
        return a

    return 0


my_int_1 = get_int(4)
print(my_int_1)  # 👉️ 0

my_int_2 = 10

print(my_int_1 > my_int_2)  # 👉️ False

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