Exercise 6.2 Stack

A stack is a data structure that you can add to and take from. Always to the top of it or from the top.

Adding to the Stack and Checking Emptiness

Create a Stack class that has a list of strings as an instance variable. Add the following methods to the class:

• is_empty() - returns a boolean-type value (true or false) that tells whether or not the stack is empty.

• add(self, value) - Adds the value given as a parameter to the top of the stack.

• values() - returns the values ​​contained in the stack as a list.

You can test your class with the following code:

s = Stack()
print(s.is_empty())
print(s.values())
s.add("Value")
print(s.is_empty())
print(s.values())

true
[]
false
[Value]

Taking from the Stack

Add to the Stack class a def take() method, which returns the topmost value (i.e., the last value added to the deque) and removes it from the stack.

s = Stack()
print(s.is_empty())
print(s.values())
s.add("Value")
print(s.is_empty())
print(s.values())
taken = s.take()
print(s.is_empty())
print(s.values())
print(taken)

true
[]
false
[Value]
true
[]
Value

s = Stack()
s.add("1")
s.add("2")
s.add("3")
s.add("4")
s.add("5")

while (not s.is_empty()):
    print(s.take())

5
4
3
2
1

Tip! When a value is added to a list, it goes to the end of the list. As such, the most recently added value is in the last index of the list - the length method provided by the list is useful for finding the last index. You can remove an element from a particular index using the pop method provided by the list.