Decimal number calculations in python

Question

I am new to Python. I have two simple questions. In my code, I need to do something like the following:

50-49.9==0.1

but python is giving False. How can I correct this? Also, a similar wrong result I am getting is in the following:

int(10*(1-0.9))

I want the answer to be 1 but I am getting 0.

Maybe reading through this documentation will be helpful https://docs.python.org/3/library/functions.html#int — Joe Ferndz, Aug 06 '20 at 05:21
What did you expect from the first equation? The second must be due to rounding errors. — Stefan, Aug 06 '20 at 05:21
all floating point truncates towards zero. So `(1-0.9)` results in `0` so `int(10*0)` will result in `0` — Joe Ferndz, Aug 06 '20 at 05:22
In this case you are checking if `50-49.9 == 0.1`. The result is not always 0.1 unless you give `round(x,1)` so it rounds to 1 decimal place — Joe Ferndz, Aug 06 '20 at 05:25

score 0 · Accepted Answer · answered Aug 06 '20 at 06:19

0

In summary, the answer to your questions.

50 - 49.9 == 0.1 will not equate to True as the left hand side is not rounded to one decimal place.
int(10*(1-0.9)) will result in int(10*0) as the equation inside an int statement always truncates towards zero. More details are in https://docs.python.org/3/library/functions.html#int

answered Aug 06 '20 at 06:19

Joe Ferndz

Number 2 is not quite correct. The problem is that 1-0.9 evaluates to 0.09999999999999998. Multiply by 10, and the value is below 1. Converting to int will remove the fraction, giving 0 – Stefan Aug 06 '20 at 14:49
... if you multiply with 100, instead of 10, it will give 9, not 0. – Stefan Aug 06 '20 at 14:52

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