Modulo operator in Python

Question

What does modulo in the following piece of code do   from math import   3 14   2   pi   How do we calculate modulo on a floating point number

User · Answer

you should use fmod a b   While abs x y   lt  abs y  is true mathematically  for floats it may not be true numerically due to roundoff    For example  and assuming a platform on which a Python float is an IEEE 754 double-precision number  in order that -1e-100   1e100 have the same sign as 1e100  the computed result is -1e-100   1e100  which is numerically exactly equal to 1e100   Function fmod   in the math module returns a result whose sign matches the sign of the first argument instead  and so returns -1e-100 in this case  Which approach is more appropriate depends on the application   where x   a b is used for integer modulo

User · Answer

Same thing you d expect from normal modulo    e g  7   4   3  7 3   4 0   3 3  Beware of floating point accuracy issues

User · Answer

same as a normal modulo  3 14   6 28   3 14  just like 3 14 4  3 14 3 14 2   1 14  the remainder

User · Answer

When you have the expression   a   b   c   It really means there exists an integer n that makes c as small as possible  but non-negative   a - n b   c   By hand  you can just subtract 2  or add 2 if your number is negative  over and over until the end result is the smallest positive number possible     3 14   2   3 14 - 1   2   1 14   Also  3 14   2   pi is interpreted as  3 14   2    pi  I m not sure if you meant to write 3 14    2   pi   in either case  the algorithm is the same  Just subtract add until the number is as small as possible

User · Answer

In addition to the other answers  the fmod documentation has some interesting things to say on the subject      math fmod x  y       Return fmod x  y   as defined by the platform C   library  Note that the Python expression x   y may not return the same   result  The intent of the C standard is that fmod x  y  be exactly    mathematically  to infinite precision  equal to x - n y for some   integer n such that the result has the same sign as x and magnitude   less than abs y   Python   s x   y returns a result with the sign of y   instead  and may not be exactly computable for float arguments  For   example  fmod -1e-100  1e100  is -1e-100  but the result of Python   s   -1e-100   1e100 is 1e100-1e-100  which cannot be represented exactly as a float  and rounds to the surprising 1e100  For this reason    function fmod   is generally preferred when working with floats  while   Python   s x   y is preferred when working with integers

[python] Modulo operator in Python

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