Decimal/Fraction input issue

Question

I'm attempting to get a user input as a fraction but use it as a decimal, in python

For example:

chance = input("Enter chance")

Let's assume the user enters "3/4"

How can I convert "3/4" to "0.75" for further calculations, such as:

total = chance + 36/67  # Where total is a float value

P.S. I'm new to python so if this seems a bad question I apologise but I couldnt find an answer anywhere.

Possible duplicate of [Math operations from string](https://stackoverflow.com/questions/9685946/math-operations-from-string) — Norman Percy, May 23 '18 at 18:50
Are you using Python 2 or 3? In Python 2 you will need to use `raw_input` instead of `input`. — Alex Hall, May 23 '18 at 19:04
@NormanPercy not a duplicate as answers to that question involve eval(), leading to security issues — TrojanHorse, May 24 '18 at 18:12
While eval can be dangerous, the question doesn't explicitly state _not_ to use eval(), and there are alternatives listed in the other thread as well. — Norman Percy, May 24 '18 at 20:44

score 2 · Accepted Answer · answered May 23 '18 at 19:20

Lets assume you've handled getting the user to input text. Then convert that text to a fractions.Fraction

>>> import fractions
>>> fractions.Fraction("3/4")
Fraction(3, 4)

You have various options from there. You could continue to use it as a Fraction but if you insist on using values of type float then simply convert to a float

>>> float(fractions.Fraction("3/4"))
0.75

MxLDevs · Answer 2 · 2018-05-23T21:46:30.333

-1

Check the input format and convert to numerator/denominator as needed before performing the necessary math operation to convert it from a fraction to a decimal value.

chance = "3/4"

# verify that format is valid, then proceed to conversion
tokens = chance.split("/")
numer = int(tokens[0])
denom = int(tokens[1])
value = numer / denom
print(value)

If you're using an older version of python (eg 2.x) you will need to convert one of the parts to a float because python discards floating point during int/int division.

edited May 23 '18 at 21:46

answered May 23 '18 at 18:57

MxLDevs

19,048
36
123
194

In addition to what Alex said: The note on the older python version (2.x) is wrong. Python never converts floats to ints. Also `/` is not an integer division. – Johannes Overmann May 23 '18 at 19:14
@JohannesOvermann In python 2, `3 / 4 ` returns 0, instead of 0.75 as it does in python 3. – MxLDevs May 23 '18 at 21:47
@JohannesOvermann "3/4 + 1" is also not valid input as far as I'm concerned and should crash in the validation step. – MxLDevs May 23 '18 at 21:49
Using python 3, this answer works perfectly fine for my purposes – TrojanHorse May 24 '18 at 17:39

Decimal/Fraction input issue

2 Answers2