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

What it means

len() counts the items in a collection, such as a string, list or dictionary. You gave it something that has no items to count, here a number. The type in the message tells you what you passed instead.

1. Counting the digits of a number

This raises the error

Broken
pin = 48213
print(len(pin))
Output
Traceback (most recent call last):
  File "<exec>", line 2, in <module>
TypeError: object of type 'int' has no len()

The fix

Fixed
pin = 48213
print(len(str(pin)))
Output
5

A number has no length, but its string does: str(48213) has 5 characters.

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2. Saving the result of `.append()`

This raises the error

Broken
names = ["Ada", "Alan"]
names = names.append("Grace")
print(len(names))
Output
Traceback (most recent call last):
  File "<exec>", line 3, in <module>
TypeError: object of type 'NoneType' has no len()

The fix

Fixed
names = ["Ada", "Alan"]
names.append("Grace")
print(len(names))
Output
3

.append() changes the list in place and returns None, which replaced the list. The message for this one says 'NoneType'. Call .append() on its own line.

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3. Calling `len()` on a `map()` result

This raises the error

Broken
numbers = map(int, "4 8 15".split())
print(len(numbers))
Output
Traceback (most recent call last):
  File "<exec>", line 2, in <module>
TypeError: object of type 'map' has no len()

The fix

Fixed
numbers = list(map(int, "4 8 15".split()))
print(len(numbers))
Output
3

map() produces items one by one and does not know how many there are. Wrapping it in list() collects them, and a list has a length. filter(), zip() and generators work the same way.

Try fixing it yourself in the editor

When you see this error, check

  • Read the type in the message: it tells you what you passed to len().
  • For the number of digits, use len(str(n)).
  • If the type is NoneType, look for a saved result of .append(), .sort() or a function without return.
  • Wrap map(), filter(), zip() and generators in list() before counting.

Related errors

All Python errors · How to read a traceback · Step through your code