2D array issue

[ritviksetty]

BPO	46093
Nosy	@ericvsmith
Files	2D-Array-Problem.py: Python File

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-12-16.07:02:09.254>
created_at = <Date 2021-12-16.05:16:24.498>
labels = ['invalid', 'type-bug', '3.8', '3.9']
title = '2D array issue'
updated_at = <Date 2021-12-16.07:02:09.252>
user = 'https://bugs.python.org/ritviksetty'

bugs.python.org fields:

activity = <Date 2021-12-16.07:02:09.252>
actor = 'eric.smith'
assignee = 'none'
closed = True
closed_date = <Date 2021-12-16.07:02:09.254>
closer = 'eric.smith'
components = []
creation = <Date 2021-12-16.05:16:24.498>
creator = 'ritviksetty'
dependencies = []
files = ['50498']
hgrepos = []
issue_num = 46093
keywords = []
message_count = 2.0
messages = ['408671', '408675']
nosy_count = 2.0
nosy_names = ['eric.smith', 'ritviksetty']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue46093'
versions = ['Python 3.8', 'Python 3.9']

[ritviksetty]

I had a problem running the following code. When I ran through what I thought python was supposed to do, I got a different answer than what python did. I think this is an error. Here is the code:

problem_ary = [['a','b','c'],['d','e','f'],['g','h','i']]
normal_ary = ['a','b','c']

print(normal_ary[:]) #should print ['a','b','c']
print(problem_ary[:][1])

The second output should be ['b','e','h'] since the print statement tells python to take [0][1],[1][1], and [2][1] from the problem_ary which is 'b','e','h'. It confused me when python instead returned ['d','e','f']. I came across this problem when I was trying to create tic-tac-toe in python. I tried coding this is Python 3.8, 3.9, and using an online interpreter, and I got the same result every time.

[ericvsmith]

problem_ary[:] creates a copy of problem_ary, so it's equal to:

>>> problem_ary[:]
[['a', 'b', 'c'], ['d', 'e', 'f'], ['g', 'h', 'i']]

The [1] element of that is:

>>> problem_ary[:][1]
['d', 'e', 'f']

So this is working as expected.

I suggest you ask on StackOverflow or the python-list mailing list if you need more help in understanding how lists work in Python.