inspection

`len (built-in)`

Returns the number of elements in the list as an int. O(1) because CPython lists track their length internally.

Syntax

len(list)

Parameters

Parameter	Purpose
(one positional)	Takes exactly the list (or any Sized object).
empty check	Prefer `if lst:` over `if len(lst) > 0:` — more Pythonic and equally correct.

>>> len([1, 2, 3])
3

Basic length.

>>> len([])
0

Empty list has length 0.

>>> len([[1, 2], [3]])
2

Counts top-level elements — does not recurse.

>>> lst = [1, 2]
>>> if lst: print('non-empty')
non-empty

Truthiness check avoids explicit len().

len() counts only top-level elements — for nested totals, use sum(len(x) for x in nested). Prefer `if lst:` over `if len(lst) > 0:`.