how to take an integer and use a fraction on it

Question

def main():
    name=input("Enter your name: ") #just write our name nothin important
    print (name, "is Swag")
    value1=int(input("enter a value: ")) #takes in the number without doubt
    print(value1)
    value2=float(int("Enter a fraction: ")) #heres our problem but what?
    print(value2)
main()

just a simple program I am playing about with but It shows this error since you all might want to know:

I write for example 1/2 an this shows

Traceback (most recent call last):
File "C:\Users\waliu\Documents\Waliur Uni stuff\Information 
systems\Python Programs\Samples\apparently fractions.py", line 8, in 
<module>
main()
File "C:\Users\waliu\Documents\Waliur Uni stuff\Information 
systems\Python Programs\Samples\apparently fractions.py", line 6, in main
value2=float(input("Enter a fraction: "))
ValueError: could not convert string to float: '1/2'

Jean-François Fabre · Answer 1 · 2017-12-02T21:25:01.870

2

python won't evaluate fractions, unless you're using eval (which is unsafe so I cannot recommend it). There are other expression evaluators like simpleeval, but in your case, if you're sure that a fraction is entered you could just split, convert to integer and divide:

>>> fraction = "1 / 2"  # input("enter a fraction")
>>> f = [int(x) for x in fraction.split("/")]
>>> f[0]/f[1]
0.5
>>>

you could handle non-fractions by just checking len(f)==2, otherwise it's either a simple integer (if len(f)==1), or an error (if > 2).

one-liner using operator.truediv & passing the args directly:

operator.truediv(*(int(x) for x in fraction.split("/")))

(no syntax check possible here obviously)

edited Dec 02 '17 at 21:25

answered Dec 02 '17 at 21:01

Jean-François Fabre

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forgot about that one. Good. I'm beginning to think that could be a duplicate. and it is, in some way: https://stackoverflow.com/questions/1806278/convert-fraction-to-float – Jean-François Fabre Dec 02 '17 at 21:22
Thanks yall for the helpouts – Dec 03 '17 at 12:44

PM 2Ring · Accepted Answer · 2017-12-02T21:23:11.677

There's a fractions module in the standard library. It can parse a string containing a representation of a fraction.

from fractions import Fraction

s = input("Enter a fraction: ")
val = Fraction(s)
print(val, float(val))

demo

Enter a fraction: 3/8
3/8 0.375

Note that the string can't contain internal spaces, but it can have spaces before or after the data.

If you want to do calculations with fractions it's a good idea to not convert them to floats, since that loses precision. And since Fraction objects use Python integers for the numerator & denominator there's no limit to how accurate they can be (apart from RAM limitations). Here's a short demo:

a = Fraction('2/3')
b = Fraction(3, 4)
c = a**2 + b**2
print(c)
print(c**10)

output

145/144
4108469075197275390625/3833759992447475122176

how to take an integer and use a fraction on it

2 Answers2