A naive stack implementation

Stack.py

class Stack:

    def __init__(self):
        self.values = []

    def push(self, x):
        self.values.append(x)

    def pop(self):
        x = self.values[-1]
        self.values.remove(x)
        return x

    def size(self):
        return len(self.values)

    def is_empty(self):
        return self.size() == 0