Same as :func:`frange`, but generator-based instead of returning a
    list.

    >>> tuple(xfrange(1, 3, step=0.75))
    (1.0, 1.75, 2.5)

    See :func:`frange` for more details.

def xfrange(stop, start=None, step=1.0):
    """Same as :func:`frange`, but generator-based instead of returning a
    list.

    >>> tuple(xfrange(1, 3, step=0.75))
    (1.0, 1.75, 2.5)

    See :func:`frange` for more details.
    """
    if not step:
        raise ValueError('step must be non-zero')
    if start is None:
        start, stop = 0.0, stop * 1.0
    else:
        # swap when all args are used
        stop, start = start * 1.0, stop * 1.0
    cur = start
    while cur < stop:
        yield cur
        cur += step