Division in Python 3 gives different result than in Python 2

Question

In the following code, I want to calculate the percent of G and C characters in a sequence. In Python 3 I correctly get 0.5, but on Python 2 I get 0

Answer 1

In python2.x / performs integers division.

>>> 3/2
1

To get desired result you can change either one of the operands to a float using float():

>>> 3/2.      #3/2.0
1.5
>>> 3/float(2)
1.5

or use division from __future__:

>>> from __future__ import division
>>> 3/2
1.5