Python dollar(float) to cents can't convert 34.8

Question

Okay am I going crazy? Run the code below, instead of being 3480 it says 3479, is this a bug? every other number works fine

def validate_dollar(dollar):
    return dollar * 100 % 1 == 0

def safe_dollar_to_cent(dollar):
    if validate_dollar(dollar):
        return {'success': True, 'cents': int(dollar*100)}
    else:
        return {'success': False, 'msg': 'Malformed input'}

print(safe_dollar_to_cent(34.8))

print(int(34.8 * 100))

Looks like floating point precision issues. https://stackoverflow.com/questions/588004/is-floating-point-math-broken is highly relevant. — Nathan Pierson, Sep 13 '20 at 06:30
And also don't use floats to represent amount of money: https://stackoverflow.com/questions/3730019/why-not-use-double-or-float-to-represent-currency — awesoon, Sep 13 '20 at 06:35
@goodvibration That's true when `x` is an integer, not true when `x` can be a float. The idea of the code being that `34.80` should be a valid amount but `34.8001` should not is reasonable. It just happens to be right along a floating precision faultline. — Nathan Pierson, Sep 13 '20 at 06:48
Use the [decimal module](https://docs.python.org/3/library/decimal.html) for money, or work only with cents, only converting to dollars for display to the user. — snakecharmerb, Sep 13 '20 at 07:55

score 0 · Answer 1 · answered Sep 13 '20 at 06:31

0

change int !! write float instead int int the line number 10 !

answered Sep 13 '20 at 06:31

Firas Chebbi

11
3

It is a float, it needs to be convert into int 3480 – givob88903 Sep 13 '20 at 06:33
aa okay ! i understang change the line number 12 : write this print(round(34.8 * 100)) – Firas Chebbi Sep 13 '20 at 06:36

score 0 · Answer 2 · edited Sep 13 '20 at 06:55

0

def validate_dollar(dollar):
     return dollar * 100 % 1 == 0

def safe_dollar_to_cent(dollar):
    if validate_dollar(dollar):
        return {'success': True, 'cents': int(dollar*100)}
    else:
        return {'success': False, 'msg': 'Malformed input'}

print(safe_dollar_to_cent(34.8))

print(round(34.8 * 100))

edited Sep 13 '20 at 06:55

Juhi Dhameliya

170
2
9

answered Sep 13 '20 at 06:38

Firas Chebbi

11
3

Python dollar(float) to cents can't convert 34.8

2 Answers2