Question

I wrote following code:

class node:
    def __init__(self, title, series, parent):
        self.series = series
        self.title = title
        self.checklist = []
        if(parent != None):
            self.checklist = parent.checklist
        self.checklist.append(self)

When I create objects like this:

a = node("", s, None)
b = node("", s, a)
print a.checklist

Unexpectedly, it shows both a and b objects as an output of print statement.
I am new to python. So, possibly there’s some stupid mistake.

Thank you.

Answer 1

You do self.checklist = parent.checklist which means that both instances share the same list. They both add themselves to it, so when you print it you see both instances.

Maybe you wanted to make a copy of the parent list? self.checklist = parent.checklist[:]