all Python 3Built-in functionsterm

sum

numbers/collections

Sums the items of an iterable. start is the initial value.

Syntax

sum(iterable, start=0)

sum refuses to concatenate strings: sum(['a', 'b']) raises TypeError about adding int and str (start defaults to 0), and sum(['a', 'b'], '') raises one that points you at ''.join(). Flattening lists with sum(lists, []) does work, but it builds a fresh list at every step and scales quadratically, so reach for itertools.chain on anything long.

Examples

print(sum([1,2,3,4,5]))  # → 15
print(sum(range(101)))  # → 5050
print(sum([[1,2],[3,4]], []))  # → [1,2,3,4]
print(sum({'a':1,'b':2}.values()))  # → 3

# Python 3.12+
print(sum([0.1]*10))  # → 1.0 — до 3.12 было 0.9999999999999999

See also

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