CODEWITHSUNDEEP
pythonlistconcatenation
user7831701
user7831701

Reputation:

Concatenate a variable number of lists in Python

I have a number of lists called: index_1, index_2, index_3, ...., index_n.
What I want is to concatenate them all in a new list.

My code so far:

index_all=[]
for i in range(1,n+1):
    index_all = index_all + globals()["index_"+str(i)]

However, I get an error:

KeyError: index_1

Any ideas as to how to solve this?

Upvotes: 1

Views: 497

Answers (4)

Aniket Navlur
Aniket Navlur

Reputation: 1012

use list unpacking

cat_list = []
for i in range(1, n+1):
    cat_list = [ *cat_list, *globals()['index_'+str(i)] ]

Upvotes: 0

Professor
Professor

Reputation: 2154

You could try this out:

list1 = [[1,2,3],[4,5,6],[7,8,9]]

def joinAll(mulist):
     index_all=[]
     for i in mulist:
         for u in i:
             index_all.append(u)
     return index_all

print joinAll(list1)

Upvotes: 1

ddor254
ddor254

Reputation: 1628

you may want to use map and filter , and the globals().items() feature:

concat_list  =  map ( lambda list_var : list_var[1] , filter ( lambda list_var  : list_var[0].startswith("list"), globals().items()))

your concat_list is the list of all items from all lists

Upvotes: 1

jwlitts
jwlitts

Reputation: 86

It seems you may just have a naming error, you try to call "index_" + str(i) but your lists are named "list_" + str(i). The following line should work as long as your lists are named list_1, list_2... list_n with no breaks and your n is correct. 

index_all = [globals()["list_"+str(i)] for i in range(1, n+1)]

If you want the lists to be flat you can 

[item for sublist in index_all for item in sublist]

It might be easier if you can avoid using globals() as it will probably be fragile!

Upvotes: 1

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