Add new gotcha

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
50/100
Issue type
Documentation
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
documentation

Research direction

No file, test, or entry point is named in the issue. Start by locating the guide section for gotchas or list mutation, then add this += versus + case; it is done when the example and safer alternative appear in the appropriate documentation section.

Written by the indexing model from the issue text.

Description

Hi,

While running tests on my code I was doing something like:

class Data:
    mylist = [1,2,3,4]


def test_function():
    local_list = Data.mylist
    local_list+=new_list

    # Do stuff with

and there are multiple tests using mylist. This is going to modify the list instead of creating a new one, an unexpected behavior of +=. This will let one test talk to the tests happening later. The safer approach is:

class Data:
    mylist = [1,2,3,4]


def test_function():
    local_list =new_list + Data.mylist

    # Do stuff with

here + will copy the list. Could you please add this case?

Cheers.

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