list inside class being appended when other object is active

Question

I'm creating a school project that needs to record the events of each iteration of a subroutine in a list. However, it appends both players list. How do I stop this from happening?

For example:

class Player:

    l = list()
    def append_list(self,i):
        self.l.append(i)

p1 = Player()
p2 = Player()

for i in range(0,5):

    p1.append_list(i)
    print(p1.l)
    p2.append_list(i)
    print(p1.l)

This code outputs:

[0]
[0, 0]
[0, 0, 1]
[0, 0, 1, 1]
[0, 0, 1, 1, 2]
[0, 0, 1, 1, 2, 2]
[0, 0, 1, 1, 2, 2, 3]
[0, 0, 1, 1, 2, 2, 3, 3]
[0, 0, 1, 1, 2, 2, 3, 3, 4]
[0, 0, 1, 1, 2, 2, 3, 3, 4, 4]

but I need it to output:

[0]
[0]
[0, 1]
[0, 1]
[0, 1, 2]
[0, 1, 2]
[0, 1, 2, 3]
[0, 1, 2, 3]
[0, 1, 2, 3, 4]
[0, 1, 2, 3, 4]

Patrick Artner · Accepted Answer · 2019-01-23T10:53:45.093

Use separate instance variables instead of shared class variables - that way each of your player instances has its own list instead of a shared one:

class Player:
    def __init__(self):
        self.l = []       # create a instance list l

    def append_list(self,i):
        self.l.append(i)

# other code identical

Output:

[0]
[0]
[0, 1]
[0, 1]
[0, 1, 2]
[0, 1, 2]
[0, 1, 2, 3]
[0, 1, 2, 3]
[0, 1, 2, 3, 4]
[0, 1, 2, 3, 4]

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list inside class being appended when other object is active

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