Method randrange

Lib/random.py:294–333

Choose a random item from range(stop) or range(start, stop[, step]). Roughly equivalent to ``choice(range(start, stop, step))`` but supports arbitrarily large ranges and is optimized for common cases.

(self, start, stop=None, step=_ONE)

    ## -------------------- integer methods  -------------------

    def randrange(self, start, stop=None, step=_ONE):
        """Choose a random item from range(stop) or range(start, stop[, step]).

        Roughly equivalent to ``choice(range(start, stop, step))`` but
        supports arbitrarily large ranges and is optimized for common cases.

        """

        # This code is a bit messy to make it fast for the
        # common case while still doing adequate error checking.
        istart = _index(start)
        if stop is None:
            # We don't check for "step != 1" because it hasn't been
            # type checked and converted to an integer yet.
            if step is not _ONE:
                raise TypeError("Missing a non-None stop argument")
            if istart > 0:
                return self._randbelow(istart)
            raise ValueError("empty range for randrange()")

        # Stop argument supplied.
        istop = _index(stop)
        width = istop - istart
        istep = _index(step)
        # Fast path.
        if istep == 1:
            if width > 0:
                return istart + self._randbelow(width)
            raise ValueError(f"empty range in randrange({start}, {stop})")

        # Non-unit step argument supplied.
        if istep > 0:
            n = (width + istep - 1) // istep
        elif istep < 0:
            n = (width + istep + 1) // istep
        else:
            raise ValueError("zero step for randrange()")
        if n <= 0:
            raise ValueError(f"empty range in randrange({start}, {stop}, {step})")
        return istart + istep * self._randbelow(n)

    def randint(self, a, b):
        """Return random integer in range [a, b], including both end points.