Python issue with an arithmetic operation

Question

I have a line of Python code that doesn't work the way it should (at least to the best of my knowledge). Following is the code line:

print 'progress: {}%'.format((i/len(e_numbers))*100)

The value of i starts from 0 and goes up to length of e_numbers which is a list, while the length of e_numbers is around 17000. But the code always prints Progress: 0%.

Any idea why?

`print 'progress: {}%'.format((float(i)/len(e_numbers))*100)` instead. Python 2.7 does integer division by default — roganjosh, Aug 19 '18 at 14:05
Well, does dividing 5 by 6 (or 6 by 8, or 1 by 2, etc) give you a floating-point number? — ForceBru, Aug 19 '18 at 14:06
@ForceBru: In python 3+, dividing 5 by 6 does give a float = `0.833333`. In python 2+ it gives 0. — Sheldore, Aug 19 '18 at 14:10
Yeah, that works. Since @roganjosh answered it first, he should post it as an answer and I'll accept it. — rootkit, Aug 19 '18 at 14:12
@Bazingaa, the OP clearly stated that they're using Python 2.7, so for them division of two integers results in another integer. — ForceBru, Aug 19 '18 at 14:12
@ForceBru: May be the above discussion will encourage the OP to update to python 3+ :) — Sheldore, Aug 19 '18 at 14:14
@rootkit there is an answer that says the same thing. You should accept that, I'm not bothered :) — roganjosh, Aug 19 '18 at 14:15
@Bazingaa I can't switch to python 3+ in this project since it's not up to me. Although, I use python 3+ in general, hence the mix up. — rootkit, Aug 19 '18 at 14:17

score 2 · Accepted Answer · answered Aug 19 '18 at 14:12

In Python 2, using / to divide two integers performs integer division by default, rounding the result down to the nearest integer value. Thus, as long as i is between 0 and len(e_numbers), i/len(e_numbers) is going to be 0. There are two possible solutions:

Cast one or both operands to a float before dividing, e.g., float(i)/len(e_numbers)
Put from __future__ import division at the top of your file so that / always produces a float.

Python issue with an arithmetic operation

1 Answers1