fspread.py

from fractions import Fraction


def fspread(count, start, end=None, step=None, mode=1):
    """Generate evenly-spaced floats.

    Yields a sequence of evenly-spaced numbers. Optional `mode` controls
    endpoint behaviour. Requires the stdlib class `fraction.Fraction`. Source:
    http://code.activestate.com/recipes/577881-equally-spaced-floats-part-2/

    Parameters
    ----------
    count : int
        Amount of subdivisions to be created. The actual amount of
        numbers can be between ``count-1`` and ``count+1`` depending
        on `mode`.
    start : float
        The starting value of the generator, included by default.
    end : float, optional
        The ending value of the generator, excluded by default.
    step : float, optional
        Size of the subdivisions to be created. A negative value results
        in decreasing numbers.
    mode : int, optional
        Switch to control endpoint behaviour:

        0 -> open interval, both `start` and `end` excluded
        1 -> half-open, `start` included and `end` excluded (default)
        2 -> half-open, `start` excluded and `end` included
        3 -> closed interval, both `start` and `end` included

    Examples
    --------
    >>> list(fspread(5, 1.0, end=2.0))
    [1.0, 1.2, 1.4, 1.6, 1.8]

    >>> list(fspread(5, 1.0, step=-0.25))
    [1.0, 0.75, 0.5, 0.25, 0.0]

    """
    if end is step is None:
        raise TypeError('one of end or step must be given')
    if not isinstance(mode, int):
        raise TypeError('mode must be an integer')
    if count != int(count):
        raise ValueError('count must be an integer')
    if count <= 0:
        raise ValueError('count must be positive')
    if mode & 1:
        yield start
    if end is None:
        step = Fraction(step)
        end = start + count*step
    else:
        step = Fraction(end-start)/count
    start = Fraction(start)
    for i in range(1, count):
        yield float(start + i*step)
    if mode & 2:
        yield float(end)