In this exercise, the
peek() methods do not have
return statements for the case where the stack is empty. What is the behavior for the methods when the stack is empty?
Python functions will default to returning the value
None if there is no explicit
return. For this exercise, the
peek() functions will print a message indicating that there is an error condition and then the methods will return with the default value. The calling code for the methods can check to see if
None is returned.