Parsing a fraction in a Django form

Question

I'm using Django on the backend and jQuery on the front end. I would like to accept both fractions and whole numbers (like "1/2", "1 1/4" or "2", for ingredient quantities in a recipe.) I'm using a FloatField to store these values. What is the best way to convert these fractions/whole numbers to floats?

score 1 · Accepted Answer · answered Nov 04 '10 at 21:48

1

>>> import fractions
>>> fractions.Fraction("1")
Fraction(1, 1)
>>> fractions.Fraction("1/2")
Fraction(1, 2)

Unfortunately, the fraction constructor doesn't handle mixed fractions ("1 1/2") so you will have to write something to parse those yourself. You can store them in the database either with a custom field or by casting them to float.

answered Nov 04 '10 at 21:48

Katriel

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Yeah, I wanted to know how to store it in the database. I was looking into overwriting the clean/to_python methods, but creating a custom field seems like the better option. – kgodey Nov 04 '10 at 22:05
Yes, I think it makes more sense to store them as fractions. Unfortunately I don't know Django, so can't help with the custom field; if you rephrase the question you might have more luck. – Katriel Nov 04 '10 at 22:27
That's fine, the Django documentation/code is pretty helpful and I got it working. Thank you! – kgodey Nov 05 '10 at 01:54

score 0 · Answer 2 · answered Jun 12 '13 at 06:24

This works for me. Could still be cleaned up a bit.

import fractions

def parse_multi_part_fraction(f):
    if '/' not in f:
        return float(f)
    parts = f.split(' ')
    total = 0.0
    for p in parts:
        if '/' in p:
            frac = fractions.Fraction(p)
            total += frac.numerator * (1.0 / frac.denominator)
        else:
            total += float(p)
    return total

Parsing a fraction in a Django form

2 Answers2