arbitrary precision number formatter

number_formatter.py

import math


def num_fmt(num):
    i_offset = 24 # change this if you extend the symbols!!!
    prec = 3
    fmt = '.{p}g'.format(p=prec)
    symbols = ['Y', 'Z', 'E', 'P', 'T', 'G', 'M', 'k', '', 'm', 'u', 'n']
    
    e = math.log10(abs(num))
    if e >= i_offset + 3:
        return '{:{fmt}}'.format(num, fmt=fmt)
    for i, sym in enumerate(symbols):
        e_thresh = i_offset - 3 * i
        if e >= e_thresh:
            return '{:{fmt}}{sym}'.format(num/10.**e_thresh, fmt=fmt, sym=sym)
    return '{:{fmt}}'.format(num, fmt=fmt)