How to append lists using list comprehension to an exsiting list

Question

I want to append items to an existing list that have been generated by list comprehension as individual lists.

source = [1,2,3,4,5]

I want the result to look like [[2], [4]]

I have tried the following (and other crazy combos of '[]' and '()' and gotten nowhere)...

target = []
target.append([r for r in source if r == 2 or r == 4])
print(target)
[[2, 4]]

target = []
target.append([[r] for r in source if r == 2 or r == 4])
print(target)
[[[2], [4]]]

target = []
target.append([r] for r in source if r == 2 or r == 4)
print(target)
[<generator object <genexpr> at 0x0000022F1986E4C8>]

Answer 1

You can use .extend() instead of .append() :

source = [1, 2, 3, 4, 5]
target = []

target.extend([r] for r in source if r == 2 or r == 4)

print(target)
# [[2], [4]]

It's possible to use .extend() in this case because it receives an iterable as an argument.

Answer 2

Just do this list comprehension with extend :

target.extend([[r] for r in source if r in [2, 4]])

And now target would be:

[[2], [4]]

Answer 3

您可以改用list.extend方法：

target.extend([r] for r in source if r == 2 or r == 4)

Answer 4

Instead of .append() go for .extend :

source = [1,2,3,4,5]
target=[]
target.extend([t] for t in source if t==2 or t==4)
print(target)

Answer 5

Just do this

source = [1,2,3,4,5]
target = [[r] for r in source if r==2 or r==4]
print(target)
# output: [[2], [4]]

If the target list is not empty and you want to append new values, you can try this

source = [1,2,3,4,5]
target = [[7],[8]]
target.extend([[r] for r in source if r==2 or r==4])
print(target)
# output: [[7], [8], [2], [4]]

or

source = [1,2,3,4,5]
target = [[7],[8]]
target += [[r] for r in source if r==2 or r==4]
print(target)
# output: [[7], [8], [2], [4]]