Fundamentals of Python: From First Programs Through Data Structures

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Fundamentals of PythonFrom First Programs
Through Data Structures

• Chapter 14
• Linear Collections Stacks

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Overview of Stacks

• Stack LIFO structure in which access is
  completely restricted to just one end, called the
  top
• Basic operations push and pop

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Using a Stack

• A stack type is not built into Python
• Can use a Python list to emulate a stack
• Use append to push and pop to pop
• Drawback stack can be manipulated by all of the
  other list operations as well
• Extra operations violate the spirit of a stack as
  an ADT
• We define a more restricted interface or set of
  operations for any authentic stack implementation
  and show how these operations are used in a brief
  example

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The Stack Interface
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So what would it take to write a Stack class
using the Python List?
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Instantiating a Stack

• We assume that any stack class that implements
  this interface will also have a constructor that
  allows its user to create a new stack instance
• Later, well consider two different
  implementations
• ArrayStack and LinkedStack
• With different performance trade-offs
• For now, assume that someone has coded these so
  we can use them
• s1 ArrayStack()
• s2 LinkedStack()