how to change " for loop" to list comprehension by Python3

Question

tokens=[[1,2,3],[4,5,6],[7,8,9]]     
for k in [m for m in tokens]:
         print(k)

how to change " for loop" to just one list comprehension by Python3?

Don't. List comprehensions are for building lists. You're not trying to build a list here. — user2357112, Jan 01 '20 at 06:28
`[m for m in tokens]` is redundant. Just use `for k in tokens:` — sshashank124, Jan 01 '20 at 06:32
@user2357112supportsMonica I think he wants to sort each elements of all 3 lists in `tokens` in a new list. — T. Feix, Jan 01 '20 at 06:39
Does this answer your question? [How do I concatenate two lists in Python?](https://stackoverflow.com/questions/1720421/how-do-i-concatenate-two-lists-in-python) — Phillip Geltman, Jan 01 '20 at 06:53

score 0 · Answer 1 · answered Jan 01 '20 at 06:38

As far as I understood your question your are trying to put every element in tokens in a new list:

kList = []                 #new empty list
for m in tokens:           #main list
    for k in m:            #sub-lists
        kList.append(k)
print(kList)               #output

score 0 · Answer 2 · edited Jan 01 '20 at 06:43

0

You could do a simple for loop to add them into one list:

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

for k in tokens:
         token_unified += (k)

print(token_unified)

Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]

edited Jan 01 '20 at 06:43

T. Feix

179
11

answered Jan 01 '20 at 06:40

Phillip Geltman

195
1
13

score 0 · Answer 3 · answered Jan 01 '20 at 06:47

0

tokens=[[1,2,3],[4,5,6],[7,8,9]]
print(*tokens, sep='\n')

Output:

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

Single line code for your expected output.

answered Jan 01 '20 at 06:47

Vashdev Heerani

660
7
21

Ladi Oyeleye · Accepted Answer · 2020-01-01T06:55:17.370

Try this:

[print(j) for i in tokens for j in i]

Or if you want it printed in list format:

print([j for i in tokens for j in i])

Edit: Not sure why this got downvoted. I assume OP's asking to print all values in the nested list using list comprehensions. If they want to return a list, you could just modify the above code to assign the list to a variable.

tokens_flattened = [j for i in tokens for j in i]

score -1 · Answer 5 · answered Jan 01 '20 at 06:48

First, try to print what your list comprehension is holding. [m for m in tokens] is nothing but your tokens. Now, whatever operation you want to perform on m for every m in tokens, perform on the first m of your list comprehension as it is a single currently selected element of the list in your loop.

The solution to your problem is as follows:

tokens=[[1,2,3],[4,5,6],[7,8,9]]
[print(m) for m in tokens]

This will give you the following output:

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

If you want to print out single elements as a list, do the following:

tokens=[[1,2,3],[4,5,6],[7,8,9]]  
ans = []   
[ans.extend(m) for m in tokens]
print(ans)

It will give you the following output:

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

how to change " for loop" to list comprehension by Python3

5 Answers5