Question

So I have a class called cell:

class cell:
    possibles = [ "1", "2", "3", "4", "5", "6", "7", "8", "9" ]
    value = None;

    def __init__(self, value):
        if value == "":
            self.value = "0"
        else:
            self.value = value

if __name__=="__main__":
    mlist = [cell("2"), cell("6"), cell("8")]
    mlist[2].possibles.remove("3")
    print mlist[0].possibles

The output is:

['1', '2', '4', '5', '6', '7', '8', '9']

Why would it remove a value from possibles in the first item of the array, when I explicitly removed it from the third item?

Answer 1

This is a common Python gotcha. The way this is written every cell has a reference to the same list instance. You can check this by printing id(mlist[i].possibles) for each i.

To create separate lists, move the initialization to the constructor:

def __init__(self, value):
    self.possibles = [ "1", "2", "3", "4", "5", "6", "7", "8", "9" ]