How to perform addition and division in python

Question

I want to get the sum of all numbers within a list. My code is shown below; however, I am getting an error when I try to run it:

c = [795557,757894,711411,556286,477322,426243,361643,350722]
for c1 in c:
   x = x + c1

I am also trying to divide one number by another. However, the result is always zero:

y=(273591/21247633)*100

Also indent correctly, also don't try to divide an integer by a tuple, also be aware of integer division. Maybe follow a tutorial? — jonrsharpe, Feb 20 '15 at 11:32
@jonrsharpe:when we perform y=(273591/21247633)*100.it will shown only 0 why? — Atul Thakre, Feb 20 '15 at 11:35
@AtuTha see e.g. http://stackoverflow.com/q/10768724/3001761 — jonrsharpe, Feb 20 '15 at 11:36
those numbers are assumed as integers.. the calcualation as float y=(float(273591)/float(21247633))*100 — Milind Dumbare, Feb 20 '15 at 11:36
@Milind you only need to convert the numerator *or* the denominator, and if you're using literals adding `.0` is fewer characters! — jonrsharpe, Feb 20 '15 at 11:36

GoBusto · Answer 1 · 2015-02-20T11:53:12.717

2

In the first case, you need to define x before you use it and use c1 instead of c:

x = 0
c=[795557,757894,711411,556286,477322,426243,361643,350722]
for c1 in c:
    x=x+c1
print x

You can try this code online here.

In the second case, you need to use floating point numbers instead of integers:

y=(273591/21247633.0)*100
print y

This is because the result of an integer-integer division in Python 2.x is also an integer. In this case, 273591 ÷ 21247633 = 0.0128763048571 so the result is rounded down to 0.

This has changed in Python 3.x, and you can enable the same behavior in Python 2.x as follows:

from __future__ import division
y=(273591/21247633)*100
print y

edited Feb 20 '15 at 11:53

answered Feb 20 '15 at 11:36

GoBusto

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Or use Python 3 which defaults to floating point division anyhow. – Antti Haapala -- Слава Україні Feb 20 '15 at 11:36
True, but this question is tagged as Python 2.7. – GoBusto Feb 20 '15 at 11:37
It is worth pointing out that this behaviour is fixed on Python 3, and beginners should be probably using it instead of Python 2 if they're doing tutorial-level learning. – Antti Haapala -- Слава Україні Feb 20 '15 at 11:41
@AnttiHaapala, I'm not sure it's "fixed" more than changed but I agree about [using python3 unless there's express reason not to](https://wiki.python.org/moin/Python2orPython3). – Holloway Feb 20 '15 at 12:25
And thanks @GoBusto for the `from __future__ import division` change. I didn't know that one. – Holloway Feb 20 '15 at 12:26

Milind Dumbare · Answer 2 · 2015-02-20T12:02:07.330

0

You forgot to initialize x to 0 and this statement should be x = x + c1 and not x = x + c

Probably those numbers are used as integers. Using their float value should help.

 y = (float(273591)/21247633)*100

edited Feb 20 '15 at 12:02

answered Feb 20 '15 at 11:38

Milind Dumbare

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what is the reason for -1? – Milind Dumbare Feb 20 '15 at 11:42
It wasn't me, but I'd guess that it's because (A) you only answered half of the question, and (B) You didn't explain *why* your answer works. What you've written in correct, though, and is arguably more explicit than simply adding `.0` on the end of the number. – GoBusto Feb 20 '15 at 11:56
I would guess that the the down-vote is due to the fact that you just posted a snippet of corrected code without any explanation what was wrong in the first place. Also, it answers only half of the question. – Adaephon Feb 20 '15 at 11:59
The other half I gave in comments ... I will update my answer though. – Milind Dumbare Feb 20 '15 at 12:00

score 0 · Answer 3 · answered Feb 20 '15 at 12:17

If you want to get a sum of numbers in a list, then use sum:

c = [795557,757894,711411,556286,477322,426243,361643,350722]
x = sum(c)

For the second one, int/int returns an int rounded down, so 273591/21247633 returns 0. Convert one (or all) of the numbers to float and it will work as awaited:

y = (273591. / 21247633.) * 100.

How to perform addition and division in python

3 Answers3