Python division

Question

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    gt  gt  gt   20-10     100-10  0   Float division doesn t work either    gt  gt  gt  float  20-10     100-10   0 0   If either side of the division is cast to a float it will work    gt  gt  gt   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

User · Answer

Make at least one of them float  then it will be float division  not integer    gt  gt  gt   20 0-10     100-10  0 1111111111111111   Casting the result to float is too late

User · Answer

It has to do with the version of python that you use  Basically it adopts the C behavior  if you divide two integers  the results will be rounded down to an integer  Also keep in mind that Python does the operations from left to right  which plays a role when you typecast   Example  Since this is a question that always pops in my head when I am doing arithmetic operations  should I convert to float and which number   an example from that aspect is presented    gt  gt  gt  a   1 2 3 4 5 4 3  gt  gt  gt  a 0   When we divide integers  not surprisingly it gets lower rounded    gt  gt  gt  a   1 2 3 4 5 4 float 3   gt  gt  gt  a 0 0   If we typecast the last integer to float  we will still get zero  since by the time our number gets divided by the float has already become 0 because of the integer division    gt  gt  gt  a   1 2 3 float 4  5 4 3  gt  gt  gt  a 0 0   Same scenario as above but shifting the float typecast a little closer to the left side    gt  gt  gt  a   float 1  2 3 4 5 4 3  gt  gt  gt  a 0 0006944444444444445   Finally  when we typecast the first integer to float  the result is the desired one  since beginning from the first division  i e  the leftmost one  we use floats   Extra 1  If you are trying to answer that to improve arithmetic evaluation  you should check this   Extra 2  Please be careful of the following scenario    gt  gt  gt  a   float 1 2 3 4 5 4 3   gt  gt  gt  a 0 0

User · Answer

Either way  it s integer division   10 90   0   In the second case  you re merely casting 0 to a float   Try casting one of the operands of     to be a float   float 20-10     100-10

User · Answer

You need to change it to a float BEFORE you do the division  That is   float 20 - 10     100 - 10

User · Answer

In Python 2 7  the   operator is an integer division if inputs are integers    gt  gt  gt 20 15 1   gt  gt  gt 20 0 15 0 1 33333333333   gt  gt  gt 20 0 15 1 33333333333   In Python 3 3  the   operator is a float division even if the inputs are integer    gt  gt  gt  20 15 1 33333333333   gt  gt  gt 20 0 15 1 33333333333   For integer division in Python 3  we will use the    operator   The    operator is an integer division operator in both Python 2 7 and Python 3 3   In Python 2 7 and Python 3 3    gt  gt  gt 20  15 1   Now  see the comparison   gt  gt  gt a   7 0 4 0  gt  gt  gt b   7 4  gt  gt  gt print a    b   For the above program  the output will be False in Python 2 7 and True in Python 3 3   In Python 2 7 a   1 75 and b   1   In Python 3 3 a   1 75 and b   1 75  just because   is a float division

User · Answer

In python cv2 not updated the division calculation  so  you must include from   future   import division  in first line of the program

User · Answer

I m somewhat surprised that no one has mentioned that the original poster might have liked rational numbers to result   Should you be interested in this  the Python-based program Sage has your back    Currently still based on Python 2 x  though 3 x is under way    sage   20-10     100-10  1 9   This isn t a solution for everyone  because it does do some preparsing so these numbers aren t ints  but Sage Integer class elements   Still  worth mentioning as a part of the Python ecosystem

User · Answer

You re using Python 2 x  where integer divisions will truncate instead of becoming a floating point number    gt  gt  gt  1   2 0   You should make one of them a float    gt  gt  gt  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    gt  gt  gt  from   future   import division  gt  gt  gt   10 - 20     100 - 10  -0 1111111111111111

User · Answer

Personally I preferred to insert a 1    at the very beginning  So the expression become something like this   1     20-10     100-10    As I always do a division for some formula like   accuracy   1     len y val  - sum y val     len y val    so it is impossible to simply add a  0 like 20 0  And in my case  wrapping with a float   may lose a little bit readability

User · Answer

You re putting Integers in so Python is giving you an integer back    gt  gt  gt  10   90 0   If if you cast this to a float afterwards the rounding will have already been done  in other words  0 integer will always become 0 float   If you use floats on either side of the division then Python will give you the answer you expect    gt  gt  gt  10   90 0 0 1111111111111111   So in your case    gt  gt  gt  float 20-10     100-10  0 1111111111111111  gt  gt  gt   20-10    float 100-10  0 1111111111111111

User · Answer

You re casting to float after the division has already happened in your second example  Try this   float 20-10    float 100-10

User · Answer

Specifying a float by placing a     after the number will also cause it to default to float     gt  gt  gt  1   2 0   gt  gt  gt  1    2  0 5

[python] Python division

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