Python float insanity

import re

EXPONENTIAL = re.compile(r'^([+-]?)([\d.]+)[eE]([+-]\d+)$')
TRAILING_ZEROS = re.compile(r'\.0*$')
def to_str(f):
    s = str(f)
    m = EXPONENTIAL.match(s)
    if not m:
        return s

    sign = m.group(1)
    digits = m.group(2).replace('.', '')
    exponent = int(m.group(3))

    if exponent < 0:
        digits = '0' * (-exponent) + digits
        exponent = 0
    else:
        digits = digits + '0' * exponent

    rv = sign + digits[:exponent + 1] + '.' + digits[exponent + 1:]
    return TRAILING_ZEROS.sub('', rv)