def trunc(f, n):
    """
    Truncates a float f to n decimal places before rounding

    :param float f: The number to truncates
    :param int n: Decimal number to place before rounding
    :returns: The corresponding truncated number
    :rtype: *float*

    """
    slen = len('%.*f' % (n, f))
    return float(str(f)[:slen])
