len() Length of object
Last updated: 2026-09-22
len() Length of object
len() returns the number of items. Works on strings, lists, tuples, dicts, sets, and any object that defines __len__.
| Category | Built-in Functions |
|---|---|
| Kind | Built-in Function |
| Python Version | all |
📝 Syntax
len(obj)⚙️ Parameters
| obj Required | An object that supports the length protocol (str, list, tuple, dict, set, etc.). |
|---|
Returns：The length (number of items) of the object, a non-negative int.
💥 Raises
TypeError— Raised when the object does not define __len__.
▶ Example
Edit the code, press Run, and see the result in the output panel:
Output：
5
4
2💡 Related Cases
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❓ FAQ
QWhy does len(generator) raise a TypeError?
AGenerators have no length (you cannot know in advance how many items they will yield). Only real containers (str/list/dict/set/tuple) and range support len(); to know the count, first list() it or count while iterating.
QWhat does len({'a': 1, 'b': 2}) return?
AIt returns 2 — a dictionary's length is the number of its keys.
QCan len() be used on an integer?
ANo — len(123) raises a TypeError: object of type 'int' has no len(). To count digits, first convert it with str(123).
QCan a custom class support len()?
AYes, implement the __len__ method; len(obj) internally calls obj.__len__().
