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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.

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  • Maybe reading through this documentation will be helpful docs.python.org/3/library/functions.html#int Commented Aug 6, 2020 at 5:21
  • What did you expect from the first equation? The second must be due to rounding errors. Commented Aug 6, 2020 at 5:21
  • all floating point truncates towards zero. So (1-0.9) results in 0 so int(10*0) will result in 0 Commented Aug 6, 2020 at 5:22
  • 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 Commented Aug 6, 2020 at 5:25
  • OK, thank you. @JoeFerndz your comment was helpful. Commented Aug 6, 2020 at 5:38

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In summary, the answer to your questions.

  1. 50 - 49.9 == 0.1 will not equate to True as the left hand side is not rounded to one decimal place.

  2. 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

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2 Comments

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
... if you multiply with 100, instead of 10, it will give 9, not 0.

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