Using Python

n this exercise you'll be completing an array-based and a link-based stack collection type discussed in this chapter. Both have similar implementations, but a link-based stack uses nodes and an array-based stack can resize the array if necessary.

In the LinkedStack class of the linkedstack.py file, complete the following:

1. Complete the implementation of the constructor method.
   • __init__, sets the initial state of self, which includes the contents of sourceCollection, if it's present.
2. Complete the implementation of the accessor methods.
   • __iter__, supports iteration over a view of self and visits items from bottom to top of stack.
   • peek(), returns the item at the top of the stack.
     • Precondition: the stack is not empty.
     • Raises: KeyError if the stack is empty.
3. Complete the implementation of the mutator methods.
   • clear(), makes self become empty.
   • push(), adds item to the top of the stack.
   • pop(), removes and returns the item at the top of the stack.
     • Precondition: the stack is not empty.
     • Raises: KeyError if the stack is empty.
     • Postcondition: the top item is removed from the stack.

In the ArrayStack class of the arraystack.py file, complete the following:

1. Complete the implementation of the constructor method.
   • __init__, sets the initial state of self, which includes the contents of sourceCollection, if it's present.
2. Complete the implementation of the accessor methods.
   • __iter__, supports iteration over a view of self and visits items from bottom to top of stack.
   • peek(), returns the item at the top of the stack.
     • Precondition: the stack is not empty.
     • Raises: KeyError if the stack is empty.
3. Complete the implementation of the mutator methods.
   • clear(), makes self become empty.
   • push(), adds item to the top of the stack.
   • pop(), removes and returns the item at the top of the stack.
     • Precondition: the stack is not empty.
     • Raises: KeyError if the stack is empty.
     • Postcondition: the top item is removed from the stack.

Verify that exceptions are raised when preconditions are violated and that the array-based implementation adds or removes storage as needed.

To test your program run the test() method in the teststack.py file.