I’m exploring Python list slicing and found an odd behavior. Can you tell me why I get this result and how do I do it right?

Question

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

# outputs 5, as expected
print(mylist[1][1])

# outputs [7,8,9] as expected
print(mylist[2])

# I want to output just col 1 only. [1,4,7]
# I know I can use a for loop or numpy for this. But
# can I do this using slice syntax? I've tried these,
# but ALL of these print the same [1,2,3]. Odd.

print(mylist[0:2][0])
print(mylist[0:-1][0])
print(mylist[0:][0])

### NOTE: I know I can accomplish this with a for loop or with numpy. I’m trying to check if it can be done with list slice syntax.

Answer 1

with only slicing you cannot...

however, there is a way between slicing and for loop... list comprehension:

col0 = [v[0] for v in mylist]

Answer 2

you may have high probabilies to get quick answer with a well formed question: accurate title, useful tags, and good description ;)

if only all (or at least most of) sololearners could post such good redacted question ^^

Answer 3

Jerry Hobby , this is also working:

print([i[0] for i in mylist]) # output is [1,4,7]

by changing the value in [0] to 1, output is [2,5,8], changing it to 2, result is [3,6,9]

Answer 4

visph That’s precisely what I was looking for. I thought I ran across a way sometime in the past. This was the method I was “trying” to remember. I appreciate your quick answer.

Answer 5

# Pythonic slicing without for loop and the output is a list in 1 line!

Feel The Power of PYTHON 💪🙏

l = [[1,2,3],[4,5,6],[6,7,8]]
elems = [l[0][0],l[1][0],l[2][0]]
print(elems)

Answer 6

Hey Jerry Hobby,
Please visit this code:-)

This is my code: https://code.sololearn.com/c81FYo8eJ8u9/?ref=app

Hope this will help you🙂

Answer 7

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