String representation of large numbers in Python

num_repr.py

import math


def num_repr(num):
    """ Return up to four digit string representation of a number, eg 2.6m """

    if num <= 9999:
        return str(num)

    digits = int(math.floor(math.log10(num)) + 1)
    sig = 3 if digits % 3 == 0 else 2
    rounded = int(round(num, int(sig - digits)))
    digits = int(math.floor(math.log10(rounded)) + 1)
    suffix = "_kmBTqXXX"[(digits - 1) // 3]
    front = 3 if digits % 3 == 0 else digits % 3

    if not front == 1:
        return str(rounded)[0:front] + suffix

    if str(rounded)[1] == "0":
        return str(rounded)[0] + suffix

    return str(rounded)[0] + "." + str(rounded)[1] + suffix