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Asked: 2026-05-15T05:43:27+00:00

When researching for this question and reading the sourcecode in random.py , I started

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When researching for this question and reading the sourcecode in random.py, I started wondering whether randrange and randint really behave as “advertised”. I am very much inclined to believe so, but the way I read it, randrange is essentially implemented as

start + int(random.random()*(stop-start))

(assuming integer values for start and stop), so randrange(1, 10) should return a random number between 1 and 9.

randint(start, stop) is calling randrange(start, stop+1), thereby returning a number between 1 and 10.

My question is now:

If random() were ever to return 1.0, then randint(1,10) would return 11, wouldn’t it?

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1 Answer

  1. Editorial Team

    From random.py and the docs:

    """Get the next random number in the range [0.0, 1.0)."""

    The ) indicates that the interval is exclusive 1.0. That is, it will never return 1.0.

    This is a general convention in mathematics, [ and ] is inclusive, while ( and ) is exclusive, and the two types of parenthesis can be mixed as (a, b] or [a, b). Have a look at wikipedia: Interval (mathematics) for a formal explanation.

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