how to concatenate lists in python?

Question

I'm trying to insert a String into a list.

I got this error:

TypeError: can only concatenate list (not "tuple") to list

because I tried this:

var1 = 'ThisIsAString' # My string I want to insert in the following list
file_content = open('myfile.txt').readlines()
new_line_insert = file_content[:10] + list(var1) + rss_xml[11:]
open('myfile.txt', 'w').writelines(new_line_insert)

The content of myfile.txt is saved in "file_content" as a list. I want to insert the String var1 after the 10th line, thats why I did

file_content[:10] + list(var1) + rss_xml[11:]

but the list(var1) doesn't work. How can I make this code work? Thanks!

You talk about inserting in a list, but you have file_content[:10] and rss_xml[11:]. First those are two different lists (and here I'm assuming that rss_xml is a list), and second you will miss out the 10th element doing that. — Mark Byers
– Mark Byers, Commented Jan 14, 2010 at 17:50

jbochi · Accepted Answer · 2010-01-14 17:45:47Z

9

try

file_content[:10] + [var1] + rss_xml[11:]

answered Jan 14, 2010 at 17:45

jbochi

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Mark Byers · Accepted Answer · 2010-01-14 17:48:15Z

3

Lists have an insert method, so you could just use that:

file_content.insert(10, var1)

answered Jan 14, 2010 at 17:48

Mark Byers

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dhg · Accepted Answer · 2010-01-14 18:18:17Z

2

It's important to note the "list(var1)" is trying to convert var1 to a list. Since var1 is a string, it will be something like:

>>> list('this')
['t', 'h', 'i', 's']

Or, in other words, it converts the string to a list of characters. This is different from creating a list where var1 is an element, which is most easily accomplished by putting the "[]" around the element:

>>> ['this']
['this']

answered Jan 14, 2010 at 18:18

dhg

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inspectorG4dget · Accepted Answer · 2010-01-14 18:17:18Z

1

file_content = file_content[:10]
file_content.append(var1)
file_content.extend(rss_xml[11:])

answered Jan 14, 2010 at 18:17

inspectorG4dget

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