Efficiently convert Decimal to whole and fractional as integers

Question

What is the best way to convert Decimal to a pair of integers to get whole and fractional in python? By saying best - I mean efficient, exact and using underlaying structure of the data type. e.g.:

d = Decimal('1536310893.687185000')
whole, fractional = some_func(d)
print(whole)
1536310893
print(fractional)
687185000

I believe there is more efficient way than to just split string representation :) I also think that Decimal is stored in memory as a pair of integers, the question is how to get them? :)

Let's start with one of the requirements - exact. What is the exact _fractional_ (you mean decimal?) value of `4/3` as an integer? — zwer, Sep 23 '18 at 06:26
So if I enter `0.25` then you want to get the fraction `1/4` ? — Nick Parsons, Sep 23 '18 at 06:27
Check this link https://stackoverflow.com/questions/6681743/splitting-a-number-into-the-integer-and-decimal-parts] — Anurag A S, Sep 23 '18 at 06:30
Do you want 123.45 and 123.045 to give the same result for the fractional part? If not, what results do you want in those cases? — Mark Dickinson, Sep 23 '18 at 20:04
Mark, good point, I did not think through it. Thanks. Then I need the same result + a number of digits after a point... — Евгений Артеменко, Sep 23 '18 at 21:32

napuzba · Answer 1 · 2018-09-23T08:13:30.430

2

Use divmod

>>> divmod(d, 1)
(Decimal('1536310893'), Decimal('0.687185000'))

edited Sep 23 '18 at 08:13

answered Sep 23 '18 at 06:40

napuzba

6,033
3
21
32

I need them as integers – Евгений Артеменко Sep 23 '18 at 06:58
Add support for integers – napuzba Sep 23 '18 at 07:37
at least looks promising. I need to know the number of digits after fixed point, and then I can make them integers – Евгений Артеменко Sep 23 '18 at 17:55

U13-Forward · Answer 2 · 2018-09-23T06:36:18.020

1

Try this using split:

d = Decimal('1536310893.687185000')
whole, fractional = map(float,str(d).split('.'))
print(whole)
print(fractional)

Output:

1536310893
687185000

Better math.modf:

import math
whole, fractional = math.modf(d)

edited Sep 23 '18 at 06:36

answered Sep 23 '18 at 06:29

U13-Forward

69,221
14
89
114

1

yeah cool, it is not efficient to convert to string :( I think decimal is stored in memory as two integers... – Евгений Артеменко Sep 23 '18 at 06:30
1

modf uses floats as output - it is not exact. I also think, Decimal is stored in memory as a pair of integers, the question is how to get them? – Евгений Артеменко Sep 23 '18 at 06:34
@ЕвгенийАртеменко Well than, i don't know how, but first solution works but inefficient tho – U13-Forward Sep 23 '18 at 06:35

Vedang Waradpande · Answer 3 · 2018-09-23T07:23:00.433

1

If you need it done by using the properties of the Decimal class you can use this function for some_func():

from decimal import *

def whole_and_fractional_part(d):
    getcontext().rounding = ROUND_FLOOR
    return d.to_integral_exact(), d - d.to_integral_exact()

This gives the output:

In [34]: whole, fractional
Out[34]: (Decimal('1536310893'), Decimal('0.687185'))

edited Sep 23 '18 at 07:23

answered Sep 23 '18 at 07:09

Vedang Waradpande

660
1
6
8

looks promising, I just need to know a number of digits after fixed point (x), and then I can multiply Fractional part by 10^x. I think It could be the most efficient. I ned to measure perforamnce... – Евгений Артеменко Sep 23 '18 at 17:54

score 1 · Answer 4 · answered Sep 23 '18 at 08:12

Decimal can be created with tuple (sign, digits, exponent) where a sign (0 for positive or 1 for negative), a tuple of digits, and an integer exponent. decimal.as_tuple() return this representation. using those options we can write the following:

def whole_frac_int(d):
    sign,digits,exp = d.normalize().as_tuple()
    return ( 
      int( decimal.Decimal( (sign,digits[:exp],0) ) ),
      int( decimal.Decimal( (sign,digits[exp:],0) ) )
    )

>>> whole_frac_int( decimal.Decimal('1536310893.687185000')
(1536310893, 687185)

Efficiently convert Decimal to whole and fractional as integers

4 Answers4