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Range lookups with bisect()

usage

An idiom from the bisect docs: bisect over a list of breakpoints yields the range index — an O(log n) table lookup instead of an if/elif chain.

Syntax

i = bisect.bisect(breakpoints, x)  # номер диапазона
labels[i]                          # метка диапазона

The label list must be exactly one longer than the list of breakpoints; otherwise extreme values raise IndexError or, worse, quietly return the wrong label. bisect() is bisect_right, so a value equal to a breakpoint falls into the upper range — switch to bisect_left if boundaries should belong to the lower one. The breakpoints themselves must be in ascending order; nothing checks that for you.

Examples

import bisect
breaks, letters = [60, 70, 80, 90], 'FDCBA'
print(letters[bisect.bisect(breaks, 33)])  # → 'F'
print(letters[bisect.bisect(breaks, 70)])  # → 'C' (граница уходит вверх)
print(letters[bisect.bisect(breaks, 89)])  # → 'B'
print(letters[bisect.bisect(breaks, 100)])  # → 'A'
print(letters[bisect.bisect_left(breaks, 70)])  # → 'D' (bisect_left оставляет границу внизу)

See also

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