TypeError: object of type 'int' has no len() (tested fix)

TypeError: object of type 'int' has no len() means you called len() on something that isn't a container. We reproduced the int, float, NoneType, generator and map variants in Python 3.13 and tested each fix.

1. len() only works on sized containers

len() needs an object with a __len__ method: str, list, tuple, dict, set, range and so on. Numbers, None and lazy iterators don't have one:

for expr in ["len(12345)", "len(3.5)", "len(None)", "len(x for x in 'ab')", "len(map(str, [1]))", "len(range(3))"]:
    try:
        print(f"{expr:22}", eval(expr))
    except TypeError as e:
        print(f"{expr:22} TypeError: {e}")

Output:

len(12345)             TypeError: object of type 'int' has no len()
len(3.5)               TypeError: object of type 'float' has no len()
len(None)              TypeError: object of type 'NoneType' has no len()
len(x for x in 'ab')   TypeError: object of type 'generator' has no len()
len(map(str, [1]))     TypeError: object of type 'map' has no len()
len(range(3))          3

2. You wanted the number of digits

n = 12345
print(len(str(n)))           # number of digits
print(len(str(-12345)))      # careful: the minus sign counts
print(len(str(abs(-12345))))

Output:

5
6
5

3. len() on an element instead of the list

items = [4, 5, 6]
try:
    for i in range(len(items[0])):     # meant len(items)
        pass
except TypeError as e:
    print("TypeError:", e)
for i, x in enumerate(items):          # usually you don't need len() at all
    print(i, x)

Output:

TypeError: object of type 'int' has no len()
0 4
1 5
2 6

len(items[0]) asks for the length of the first element, an int. Usually enumerate() removes the need for range(len(...)) entirely.

4. NoneType has no len(): a function returned nothing

def find_rows(rows):
    if rows:
        return rows
    # falls off the end -> returns None
try:
    len(find_rows([]))
except TypeError as e:
    print("TypeError:", e)
print(len(find_rows([]) or []))

Output:

TypeError: object of type 'NoneType' has no len()
0

A function that falls off the end returns None. Fix the function so it always returns a list, or fall back with or []. Methods like list.sort() also return None; see NoneType object has no attribute.

5. Generators, map and filter have no length

squares = (x * x for x in range(5))
print(len(list(squares)))           # materialise first...
print(len(list(squares)))           # ...but a generator can only be consumed once
print(sum(1 for _ in (x for x in range(5))))   # count without building a list

Output:

5
0
5

Converting to a list consumes the generator: the second len(list(squares)) is 0. Keep the list if you need it again, or count with sum(1 for _ in ...) when you only need the count.

6. Your own class

class Cart:
    def __init__(self): self.items = ["a", "b"]
try:
    len(Cart())
except TypeError as e:
    print("TypeError:", e)
class Cart2(Cart):
    def __len__(self): return len(self.items)
print(len(Cart2()), bool(Cart2()))

Output:

TypeError: object of type 'Cart' has no len()
2 True

Defining __len__ also makes empty instances falsy. Related: object is not iterable.

Written with AI assistance. Measured on 2026-10-22 on Debian with Python 3.13.5: len() on int, float, None, generator and map; digit counting; len of an element; functions returning None; consumed generators and __len__. Every block was run verbatim and its output pasted unedited. PlainHeaders is our extension; Python is free.