Question

I have a Python 3 class method for rescaling values that looks like this:

class A(object):
    """docstring for A"""
    def __init__(self):
        super(A, self).__init__()

    def rescale(self, old_min, old_max, new_min, new_max, value):
         """rescales a value given a current old_min and 
         old_max to the desired new_min and new_max"""
         scale = (old_max - old_min) / (new_max - new_min)
         rescaled_value = new_min + ((value - old_min) / (scale))
         return rescaled_value 

Using Python 3, this method works like this:

>>> import A
>>> x = A()
>>> x.rescale(1,10,1,100,5)
45.0

In Python 2.7, this code does not work:

>>> from __future__ import division
>>> x = A()
>>> x.rescale(1,10,1,100,5)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "bunsen.py", line 35, in rescale
rescaled_value = new_min + ((value - old_min) / (scale))
ZeroDivisionError: integer division or modulo by zero

If I manually do this math in Python 2.7 I get the correct answer:

>>> from __future__ import division
>>> scale = (10 - 1) / (100 - 1)
>>> rescaled_value = 1 + ((5 - 1) / (scale))
>>> rescaled_value
45.0

Can anyone point out why this method does not work in Python 2.7?

Answer 1

You need to set from __future__ import division in the file that contains the divisions, i.e. in the file with A.