Python append to an string element in a list

Question

I'm fairly new to python. I want to know how can you append to a string element in a list cumulatively ?

list = ['1','2','3','4']
list2 = ['a','b','c','d']

I want a new list like this:

list3 = ['1a', '1b', '1c', '1d']

I've been running circles for possible answers. Help is much appreciated, thanks !

do you want `list3 = ['1a', '1b', '1c', '1d']` or `list3 = ['1a', '2b', '3c', '4d']`? — joel goldstick, Jul 09 '16 at 20:02
Your result is bit misleading. DO you want to prefix `1` with all the elements of list2 or is it an adjacent concatenation? — Abhijit, Jul 09 '16 at 20:02
Are you sure you want `['1a', '1b', '1c', '1d']` and not `['1a', '2b', '3c', '4d']`? — cmmnn, Jul 09 '16 at 20:04

score 2 · Answer 1 · edited May 23 '17 at 11:51

2

Using list comprehension. Note that you need to turn the integer into a string via the str() function, then you can use string concatenation to combine list1[0] and every element in list2. Also note that list is a keyword in python, so it is not a good name for a variable.

>>> list1 = [1,2,3,4]
>>> list2 = ['a','b','c','d']
>>> list3 = [str(list1[0]) + char for char in list2]
>>> list3
['1a', '1b', '1c', '1d']

edited May 23 '17 at 11:51

Community

1
1

answered Jul 09 '16 at 19:58

ifma

3,673
4
26
38

While code often speaks for itself, it's good to add some explanation to your code. – Will Jul 09 '16 at 19:59

score 2 · Accepted Answer · edited Jul 09 '16 at 20:07

2

You can use map() and zip like so:

list = ['1','2','3','4']
list2 = ['a','b','c','d'] 

print map(lambda x: x[0] + x[1],zip(list,list2))

Output:

['1a', '2b', '3c', '4d']

Online Demo - https://repl.it/CaTY

edited Jul 09 '16 at 20:07

Will

24,082
14
97
108

answered Jul 09 '16 at 19:59

Jossef Harush Kadouri

32,361
10
130
129

score 1 · Answer 3 · answered Jul 09 '16 at 20:05

In your question you want list3 = ['1a', '1b', '1c', '1d'].

If you really want this: list3 = ['1a', '2b', '3c', '4d'] then:

>>> list = ['1','2','3','4']
>>> list2 = ['a','b','c','d'] 
>>> zip(list, list2)
[('1', 'a'), ('2', 'b'), ('3', 'c'), ('4', 'd')]
>>> l3 = zip(list, list2)
>>> l4 = [x[0]+x[1] for x in l3]
>>> l4
['1a', '2b', '3c', '4d']
>>>

score -2 · Answer 4 · answered Jul 09 '16 at 21:40

I'm assuming your goal is [ '1a', '2b', '3c', '4d' ] ?

list = [ '1', '2', '3', '4' ]
list2 = [ 'a', 'b', 'c', 'd' ]
list3 = []

for i in range (len(list)):
    elem = list[i] + list2[i]
    list3 += [ elem ]

print list3

In general though, I'd be careful about doing this. There's no check here that the lists are the same length, so if list is longer than list2, you'd get an error, and if list is shorter than list2, you'd miss information.

I would do this specific problem like this:

letters = [ 'a', 'b', 'c', 'd' ]
numberedLetters = []

for i in range (len(letters)):
    numberedLetters += [ str(i+1) + letters[ i ] ]

print numberedLetters

And agree with the other posters, don't name your variable 'list' - not only because it's a keyword, but because variable names should be as informative as reasonably possible.

Python append to an string element in a list

4 Answers4