Unable to do code with list in python

Question

I am new to python and learning from CodeAcademy.com; I have a problem:

Change list_function so that:

Add 3 to the item at index one of the list.

Store the result back into index one.

Return the list.

Here is my code:

def list_function(x):
    return x

n = [3, 5, 7]
n.insert(1,3)
print list_function(n)

I get only the error, what should i do?

My problem is to understand the number 2 and 3 option.

If you're using python 3 I think you need to use print with function syntax i.e print(list_function(n)) — John Greenall
– John Greenall, Commented Jan 15, 2015 at 8:41
@MartijnPieters - trying to be helpful! when I tried following a dive into python tutorial years ago I was using python 3 and got stuck for half an hour wondering why i couldn't get "hello world" to work! — John Greenall
– John Greenall, Commented Jan 15, 2015 at 8:45
@MarounMaroun: ah, yes, misunderstood what you meant. You may want to be explicit about please post the error you got here next time. CodeAcademy gives the student a message that their solution is wrong, I believe, but there was no Python exception here. — Martijn Pieters
– Martijn Pieters, Commented Jan 15, 2015 at 9:04

Martijn Pieters · Accepted Answer · 2015-01-15 09:05:17Z

2

You are confusing adding with inserting, point 1:

Add 3 to the item at index one of the list.

You interpreted this as insertion:

n.insert(1,3)

but really they meant the arithmetic operation:

n[1] + 3

This adds 3 (with +) tot the item at index one ([1]) of the list (n).

You then insert that back into the list at the same index:

n[1] = n[1] + 3

All this should be done inside your function:

def list_function(some_list):
    some_list[1] = some_list[1] + 3  # step 1 and 2
    return some_list                 # step 3

edited Jan 15, 2015 at 9:05

answered Jan 15, 2015 at 8:45

Martijn Pieters

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1 Comment

Frerich Raabe Over a year ago

Spot on; the question was triggered by the overloaded meaning of add. For the record, if you are willing to combine step 1 and 2 into a single statement you might consider using some_list[1] += 3 (though this might be considered 'less explicit' about what's going on).

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