Python division

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I was trying to normalize a set of numbers from -100 to 0 to a range of 10-100 and was having problems only to notice that even with no variables at all, this does not evaluate the way I would expect it to:

>>> (20-10) / (100-10)
0
Float division doesn't work either:

>>> float((20-10) / (100-10))
0.0
If either side of the division is cast to a float it will work:

>>> (20-10) / float((100-10))
0.1111111111111111
Each side in the first example is evaluating as an int which means the final answer will be cast to an int. Since 0.111 is less than .5, it rounds to 0. It is not transparent in my opinion, but I guess that's the way it is.

What is the explanation?
Oct 12, 2018 in Python by ana1504.k
• 7,870 points
44 views

1 answer to this question.

0 votes
You're using Python 2.x, where integer divisions will truncate instead of becoming a floating point number.

>>> 1 / 2
0
You should make one of them a float:

>>> float(10 - 20) / (100 - 10)
-0.1111111111111111
or from __future__ import division, which the forces / to adopt Python 3.x's behavior that always returns a float.

>>> from __future__ import division
>>> (10 - 20) / (100 - 10)
-0.1111111111111111
answered Oct 12, 2018 by SDeb
• 13,180 points

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