|
Size: 1465
Comment:
|
Size: 913
Comment:
|
| Deletions are marked like this. | Additions are marked like this. |
| Line 28: | Line 28: |
| -3 is the correct answer to the expression -25/12 Here is why. Consider the statement print 25/12 and print 25%12 {{{>>> print 25/12 2 >>> print 25%12 1}}} This is because 25 = 2 * '''12''' + 1 So print -25/12 and print -25%12 gives you {{{>>> print -25/12 -3 >>> print -25%12 11}}} Because -25 = -3 * '''12''' + 11 Your suggested answer -25/12 = -2 implies that -25%12 = -1 -25 = -2 * '''12''' + -1 But the result of A%B must be positive so -25%12 = 11 instead of -1 thus -25/12 must be -3 instead of -2 ---- |
I discovered this when my students were creating a fraction class. 7/4 = 1 however -7/4 = -2 It seems to me the second result should be -1 It appears it is using the floor function but it isn't what my students wanted nor can I think of when anyone would want this result. Anyone know why? Thanks for any help Terry S - tscott@fisher.unco.edu
That is what floor division does, it reduces the value to the next lowest whole number. If you want to separate the whole number and fractional part, use math.modf:
from __future__ import division import math print math.modf(25/12) --> (0.08333, 2.0) print math.modf(-25/12) --> (-0.08333, -2.0) #to just print the whole number as an int: print int(math.modf(25/12)[1])
Please see the Python Programming FAQ, [http://www.python.org/doc/faq/programming.html#why-does-22-10-return-3 question 1.3.2], for an explanation.