How does the python function int() work such that it produces strange anomalies?

Asked Nov 03 '15 at 05:49

Active Nov 03 '15 at 05:49

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Why does the following statement in Python output the integer 19 rather than 20?

int((11.20-11)*100)

I believe there is something about the int function that I do not know about. How is the int function programmed such that the above line of code outputs 19?

asked Nov 03 '15 at 05:49

Rohan

2

Because `0.20` cannot be accurately represented in floating point. – Martijn Pieters Nov 03 '15 at 05:51
Check the output of 11.20-11, and you'll find its `0.1999999999999993` – Burhan Khalid Nov 03 '15 at 05:54
Why does that happen? – Rohan Nov 03 '15 at 05:56
Maybe this documentation could help: https://docs.python.org/2/tutorial/floatingpoint.html – Foad Tahmasebi Nov 03 '15 at 05:57
Or this: https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html – Geoffrey Nov 03 '15 at 05:59
I suggest learning about "floating point" numbers. In this case, 0.20 cannot be exactly represented as a finite sum of powers of two, so its representation is an approximation, not exact. This is true in any computer language that supports floating point numbers. – Tom Karzes Nov 03 '15 at 06:09

How does the python function int() work such that it produces strange anomalies?

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