finding smallest number in list for python

Question

I am trying to use a for loop to get an average for each week and for the month in python:

sum = 0
sumA = 0
sumB = 0
sumC = 0
sumD = 0

week1 = (35,38,30,34,27,40,39)
week2 = (35,38,30,34,27,40,39)
week3 = (35,38,30,34,27,40,39)
week4 = (35,38,30,34,27,40,39)

for x in (week1):
    sum = sum + week1[x]
    avg1 = (sum + week1[x]) / 7
for y in (week2):
    sumA = sumA + week2[y]
    avg2 = (sumA + week2[y]) / 7
for z in (week3):
    sumB = sumB + week3[z]
    avg3 = (sumB + week3[z]) / 7
for k in (week4):
    sumC = sumC + week4[k]
    avg4 = (sumC + week4[k]) / 7

sumD = sum + sumA + sumB + sumC
avg = (sum + sumA + sumB + sumC) / 28

that is it but its not correct. can i get some help please

not a good idea to use 'sum', as it's a builtin function. and if a 'for' loop isn't required, you could make a much simpler, more maintainable script using 'sum'. — jcomeau_ictx
– jcomeau_ictx, Commented Apr 4, 2011 at 19:33
for loops in Python can be considered a code smell, especially when it's for calculating a numeric quantity. Python lends itself more to a functional approach. See e.g. map/reduce docs.python.org/library/functions.html — I82Much
– I82Much, Commented Apr 4, 2011 at 19:33
@I28Much: No, they're not "code smells", they're an important part of the language and used well in a billion functions. Not using builtin functions when appropriate, on the other hand, is indeed no good. — user395760
– user395760, Commented Apr 4, 2011 at 19:36

Sven Marnach · Accepted Answer · 2011-04-04 19:32:34Z

5

Assuming you are using Python 2.x, the / operator for two integers uses integer divsion, i. e. the result of the division is rounded down to the next integer. Try it in the interactive interpreter:

>>> 5/3
1

To get the correct floating point division, either use

from __future__ import division

or convert one of the operands to float first

avg = float(sum + sumA + sumB + sumC) / 28

answered Apr 4, 2011 at 19:32

Sven Marnach

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Comments

ChristopheD · Accepted Answer · 2011-04-04 20:07:44Z

4

You don't need these loops. Here's a quick example:

>>> week1 = (35,38,30,34,27,40,39)
>>> average1 = sum(week1) / len(week1)
>>> average1
34

As in the comments:

The above example (in Python 2.x) needs one part cast to float if you want 'true' division (e.g. 34.71).

In Python 3.x the single / division defaults to 'true' division so the above snippet would be correct (although with a different resulting value for average1).

edited Apr 4, 2011 at 20:07

answered Apr 4, 2011 at 19:32

ChristopheD

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5 Comments

Fred Foo Over a year ago

Except that the average is really 34.71.

user691693 Over a year ago

I have to use a pair of nested for loops

Mr_Pink Over a year ago

@ChristopheD - No, // is integer division - you should have done something like float(sum(week1))/len(week1)

ChristopheD Over a year ago

@user691693: Seriously? Then you might want to consider adding a homework tag.

Mr_Pink Over a year ago

@user691693 - why? if this is homework, please tag it as such

Fred Foo · Accepted Answer · 2011-04-04 19:32:58Z

3

There are several problems here. First, for x in lst yields the elements of lst, not the indices. Second, you add in the elements twice, once when updating sum, then again when updating avg. Just compute avg outside the list. Third, divide by a float instead of an int to prevent truncation:

for x in (week1):
    sum = sum + x
avg1 = sum / 7.

answered Apr 4, 2011 at 19:32

Fred Foo

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Comments

I82Much · Accepted Answer · 2011-04-04 20:31:32Z

2

list = [....]
avg = sum(list)/float(len(list))

edited Apr 4, 2011 at 20:31

answered Apr 4, 2011 at 19:32

I82Much

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Comments

jcomeau_ictx · Accepted Answer · 2011-04-04 19:39:56Z

1


>>> def ave(numbers):
...  return sum(numbers) / len(numbers)
... 
>>> week1 = (35,38,30,34,27,40,39)
>>> week2 = (35,38,30,34,27,40,39)
>>> week3 = (35,38,30,34,27,40,39)
>>> week4 = (35,38,30,34,27,40,39)
>>> ave(week1)
34
>>> ave(week1+week2+week3+week4)
34
>>>

As others pointed out, use from __future__ import division if you want a non-truncated result

answered Apr 4, 2011 at 19:39

jcomeau_ictx

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