Python Decimal - engineering notation for mili (10e-3) and micro (10e-6)

Question

Here is the example which is bothering me:

>>> x = decimal.Decimal('0.0001')
>>> print x.normalize()
>>> print x.normalize().to_eng_string()
0.0001
0.0001

Is there a way to have engineering notation for representing mili (10e-3) and micro (10e-6)?

Answer 1

Here's a function that does things explicitly, and also has support for using SI suffixes for the exponent:

def eng_string( x, format='%s', si=False):
    '''
    Returns float/int value <x> formatted in a simplified engineering format -
    using an exponent that is a multiple of 3.

    format: printf-style string used to format the value before the exponent.

    si: if true, use SI suffix for exponent, e.g. k instead of e3, n instead of
    e-9 etc.

    E.g. with format='%.2f':
        1.23e-08 => 12.30e-9
             123 => 123.00
          1230.0 => 1.23e3
      -1230000.0 => -1.23e6

    and with si=True:
          1230.0 => 1.23k
      -1230000.0 => -1.23M
    '''
    sign = ''
    if x < 0:
        x = -x
        sign = '-'
    exp = int( math.floor( math.log10( x)))
    exp3 = exp - ( exp % 3)
    x3 = x / ( 10 ** exp3)

    if si and exp3 >= -24 and exp3 <= 24 and exp3 != 0:
        exp3_text = 'yzafpnum kMGTPEZY'[ ( exp3 - (-24)) / 3]
    elif exp3 == 0:
        exp3_text = ''
    else:
        exp3_text = 'e%s' % exp3

    return ( '%s'+format+'%s') % ( sign, x3, exp3_text)