Storing all values of a changing variable in a for loop

Question

I have a variable called CurrentLineup, which contains a set of 5 names as such

set(['Player 1', 'Player 2', 'Player 3', 'Player 4', 'Player 5'])

I have a loop of all of the events during a game, which includes other players' substitutions in and out of the game.

What I would like to do is create a list of all 5 man sets as CurrentLineup updates, so I initialized the following outside of the loop... take this code as an example.

Lineup_List = []
Lineup_List.append(Current_Lineup)

For i in game_events:
    if "Enters Game" in i:
        player = 'Player 6'
        Current_Lineup.add(player)
    if "Leaves Game" in i:
        player2 = 'Player 4'
        Current_Lineup.remove(player2)
    if len(Current_Lineup) == 5:
        Lineup_List.append(Current_Lineup)

My problem is that when I return Lineup_List after the loop, it has the final version of Current_Lineup a number of times.

If this loop ran twice, I would hope for Lineup_List to have the following result:

[set(['Player 1', 'Player 2', 'Player 3', 'Player 4', 'Player 5']), 
 set(['Player 1', 'Player 2', 'Player 3', 'Player 6', 'Player 5'])]

How do I retain the various values that CurrentLineup takes through the loop, in order of occurrence?

the list stores a reference to the very same set multiple times. you can append(copy.deepcopy(myset)) to store a copy, not the original — deeenes
– deeenes, Commented Feb 7, 2017 at 18:58
It is probably not needed (or even desirable) to perform a deep copy. A shallow copy should be what is needed. — trincot
– trincot, Commented Feb 7, 2017 at 19:01

trincot · Accepted Answer · 2017-02-07 19:42:39Z

2

You need to make a (shallow) copy of the set when you append it, otherwise you just keep changing the same set, also when already referenced in the line up list. So change the last line as follows (add set()):

Lineup_List.append(set(Current_Lineup))

This appends a copy of your current line up set, so that you can safely change it in the next iterations without affecting the already added set(s).

edited Feb 7, 2017 at 19:42

answered Feb 7, 2017 at 19:00

trincot

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5 Comments

BSHuniversity Over a year ago

Thanks for your answer @trincot. I get the following error with your suggestion: TypeError: 'set' object has no attribute 'getitem'. Thoughts?

trincot Over a year ago

Ah, I missed the part where you said it was a set. I understood it to be a list. I updated my answer accordingly.

BSHuniversity Over a year ago

Sorry for the back and forth... but here's the newest error with your updated answer. "NameError: global name 'Current_Lineup' is not defined"

trincot Over a year ago

Your question does not have the code for the initial assignment to Current_Lineup, and you have For written with a capital, which is invalid syntax. But besides that, it works: repl.it/FaiY

BSHuniversity Over a year ago

Got it. Thanks so much for your help.

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