September 18, 2026

AttributeError: 'NoneType' object has no attribute 'X' — What It Means

This error means you called a method on a value that turned out to be None — usually because a function didn't return what you expected it to.

main.py

Try it yourself →

def find_first_even(numbers):
    for n in numbers:
        if n % 2 == 0:
            result = n

numbers = [1, 3, 5]
first_even = find_first_even(numbers)
print(first_even.bit_length())

Output

Traceback (most recent call last):
  File "script.py", line 8, in <module>
    print(first_even.bit_length())
AttributeError: 'NoneType' object has no attribute 'bit_length'

Why this happens

find_first_even() has no return statement at all — it just assigns to a local variable called result and never sends anything back. Every function without an explicit return implicitly returns None, no matter what happened inside it. first_even ends up as None, and calling .bit_length() on it fails.

The fix

main.py

Try it yourself →

def find_first_even(numbers):
    for n in numbers:
        if n % 2 == 0:
            return n
    return None

numbers = [1, 3, 5, 4]
first_even = find_first_even(numbers)
if first_even is not None:
    print(first_even.bit_length())
else:
    print("No even number found")

Output

return exits the function immediately with the value that was actually found. Checking if first_even is not None before using the result means the program handles the "nothing found" case on purpose, instead of crashing on it.

This exact shape of bug — a missing return causing a silent None — is common enough that it's worth checking first whenever you see 'NoneType' object has no attribute. See the Functions lesson in our free Python course for more on return values.

Read the full Functions lesson →