# len `len` is a [[Built-in|builtin]] [[Function]] used to get the size of a data-structure. On Python [[Built-in|builtins]] types, `len` has a time complexity of O(1).[^1] --- Bibliography: - [Cost of len() function - stackoverflow.com](https://stackoverflow.com/q/1115313/6251742) - [Understanding python's len() time complexity - stackoverflow.com](https://stackoverflow.com/q/71684970/6251742) [^1]: https://wiki.python.org/moin/TimeComplexity#list