python add objects from list into another list

Question

I have not found an answer to my question: (maybe not the words to found it) I have two lists, I would like to add each element (and keep the order) to another list. For example:

A = ["abc", "def", "ghi"]
B = ["123", "456", "789"]

result = ["abc123", "def456", "ghi789"]

Thanks

sundar nataraj · Accepted Answer · 2014-06-03T07:42:45.723

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result=[]
for i,j in zip(A,B):
        result.append(i+j)

also:
map(lambda x : x[0]+x[1],zip(A,B))

list comprehension we can acheive it in single line

[ x+y for x,y in zip(A,B)]

explanation: above code is a list in which elements are x+y from the zip(A,B)

edited Jun 03 '14 at 07:42

answered Jun 03 '14 at 07:32

sundar nataraj

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Thanks, I'm beginner so I understand the first one. I choose it ! – Guillaume Jun 03 '14 at 07:39

score 2 · Answer 2 · answered Jun 03 '14 at 07:33

2

result = [ a + b for a, b in zip(A, B) ]

Even better (using a generator instead of an intermediate list):

from itertools import izip
result = [ a + b for a, b in izip(A,B) ]

answered Jun 03 '14 at 07:33

Oleg Sklyar

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score 1 · Answer 3 · answered Jun 03 '14 at 07:34

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result = [ str(a)+str(b) for a, b in zip(A, B) ]

Thanks to str() usage, you can have lists of any objects, not only strings, and your result will be list of strings.

answered Jun 03 '14 at 07:34

Filip Malczak

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why converting string to again string – sundar nataraj Jun 03 '14 at 07:35
Thanks to that you can use A = [1, 2, 3] and it won't fail. I've explained, that it will allow any type of lists elements. – Filip Malczak Jun 03 '14 at 07:49

score 1 · Answer 4 · answered Jun 03 '14 at 07:34

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One liner:

map (lambda t: t[0]+t[1], zip(A,B))

answered Jun 03 '14 at 07:34

Freek Wiekmeijer

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No need for a *lambda*. Use the operator module instead: ``map(add, A, B)``. – Raymond Hettinger Jun 03 '14 at 07:36

score 1 · Answer 5 · answered Jun 03 '14 at 07:36

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An alternative way would be using operator.__add__ and map().

from operator import __add__

A = ["abc", "def", "ghi"]
B = ["123", "456", "789"]

print map(__add__, A, B)

answered Jun 03 '14 at 07:36

Christian Tapia

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why adding a module? I have already so much in my program – Guillaume Jun 03 '14 at 07:40
`from operator import __add__` will only import the built-in function `__add__`, not the whole module. Also, this approach [has the advantage that is faster than others](http://stackoverflow.com/a/18713344/2670792), except for a numPy solution. – Christian Tapia Jun 03 '14 at 07:42
Ok, thanks for the precision – Guillaume Jun 03 '14 at 07:45

python add objects from list into another list

5 Answers5