'Create a unique suffix.
This creates a suffix based on the number given as ``iteration``. It
will return a value encoded as lowercase ascii letter. So we have an
alphabet of 26 letters. The returned suffix will be for example ``_yh``
where ``yh`` is the encoding of ``iteration``. The length of it will be
``math.log(iteration, 26)``.
Examples::
uniquifying_suffix(0) == \'_a\'
uniquifying_suffix(25) == \'_z\'
uniquifying_suffix(26) == \'_ba\'
uniquifying_suffix(52) == \'_ca\''

def uniquifying_suffix(self, iteration):

    alphabet = string.ascii_lowercase
    length = len(alphabet)
    if (iteration == 0):
        power = 0
    else:
        power = int(math.log(iteration, length))
    current = iteration
    suffix = ''
    for exp in reversed(list(range(0, (power + 1)))):
        digit = int(truediv(current, (length ** exp)))
        suffix += alphabet[digit]
        current = (current % (length ** exp))
    return '_{suffix}'.format(suffix=suffix)
