Key of the largest or smallest value

Find the key with the largest or smallest value using max() or min() with a key function.

Which product sold most? max(d.values()) gives the number but not the product. Rank the keys by value instead.

key_of_max.py✓ ruff · mypy --strict

from collections.abc import Mapping
from typing import Any, Protocol, TypeVar


class _SupportsLessThan(Protocol):
    def __lt__(self, other: Any, /) -> bool: ...


K = TypeVar("K")
V = TypeVar("V", bound=_SupportsLessThan)


def key_of_max(d: Mapping[K, V]) -> K:
    """Return the key of the largest value in ``d``; on a tie, the first one."""
    return max(d, key=d.__getitem__)


def key_of_min(d: Mapping[K, V]) -> K:
    """Return the key of the smallest value in ``d``; on a tie, the first one."""
    return min(d, key=d.__getitem__)

iterating a dict yields keys; key= ranks them by value

examples✓ 3 doctests · 3.11–3.14

✓passed on Python 3.11 to 3.14: >>> key_of_max({"a": 4, "b": 0, "c": 13})'c'✓passed on Python 3.11 to 3.14: >>> key_of_max({"x": 1, "y": 1})'x'✓passed on Python 3.11 to 3.14: >>> key_of_min({"a": 4, "b": 0, "c": 13})'b'

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key_of_max.py

examples · doctest

How it works

Iterating a dict yields its keys.
key=d.__getitem__ ranks each key by its value.
On a tie, max and min return the first key, in dict order. An empty dict raises ValueError.

Key of the largest or smallest value

How it works

Related