class Stack:
def __init__(self):
self.__data = []
def empty(self):
return len(self.__data) == 0
def size(self):
return len(self.__data)
def push(self, x):
self.__data.append(x)
def pop(self):
return self.__data.pop()
stack = Stack()
stack.push(10)
stack.push(15)
stack.push(20)
print(stack.empty())
print(stack.size())
print(stack.pop())
print(stack.pop())
print(stack.pop())
print(stack.empty())
print(stack.size())
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