truncate_digits

import decimal


def truncate(num, lim):
    """Truncates/pads a float f to n decimal places without rounding."""
    snum = "{}".format(num)

    if 'e' in snum or 'E' in snum:
        snum = "{0:f}".format(num)

    (intg, pt, dec) = snum.partition('.')

    numlen = len(intg) + len(dec)

    if len(intg) < lim:
        if numlen >= lim:
            diff = lim - len(intg)
            fnum = intg + '.' + dec[0:diff]
        else:
            fnum = intg + '.' + dec + '0' * (lim - numlen)
    elif len(intg) == lim:
        fnum = intg
    else:
        fnum = intg[0:lim]

    return decimal.Decimal(fnum)