"""
Arithmetic progression generator function::

    >>> ap = aritprog_gen(1, .5, 3)
    >>> list(ap)
    [1.0, 1.5, 2.0, 2.5]
    >>> ap = aritprog_gen(0, 1/3, 1)
    >>> list(ap)
    [0.0, 0.3333333333333333, 0.6666666666666666]
    >>> from fractions import Fraction
    >>> ap = aritprog_gen(0, Fraction(1, 3), 1)
    >>> list(ap)
    [Fraction(0, 1), Fraction(1, 3), Fraction(2, 3)]
    >>> from decimal import Decimal
    >>> ap = aritprog_gen(0, Decimal('.1'), .3)
    >>> list(ap)
    [Decimal('0'), Decimal('0.1'), Decimal('0.2')]

"""


# tag::ARITPROG_GENFUNC[]
def aritprog_gen(begin, step, end=None):
    result = type(begin + step)(begin)
    forever = end is None
    index = 0
    while forever or result < end:
        yield result
        index += 1
        result = begin + step * index
# end::ARITPROG_GENFUNC[]