115 lines
2.9 KiB
Python
115 lines
2.9 KiB
Python
######################################
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# DCS 229 -- Stack
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# Stack data structure implemented with Linked List
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# Date:
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# Name:
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# Resources Used: LinkedList.py from Project 4. I also worked with Pat Cohen on the project.
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##########################################
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from LinkedList import *
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class EmptyError(Exception):
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''' class extending Exception to better document stack errors '''
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def __init__(self, message: str):
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self.message = message
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class Stack[T]:
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''' class to implement a stack ADT using our LinkedList class'''
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def __init__(self):
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''' initializes an empty stack '''
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self._data = LinkedList()
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def __len__(self) -> int:
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''' allows the len function to be called using an ArrayStack object, e.g.,
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stack = ArrayStack()
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print(len(stack))
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Returns:
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number of elements in the stack, as an integer
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'''
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return len(self._data)
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def push(self, item: T) -> None:
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''' pushes a given item of arbitrary type onto the stack
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Parameters:
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item: an item of arbitrary type
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Returns:
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None
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'''
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self._data.insert_head(item)
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def pop(self) -> T:
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''' removes the topmost element from the stack and returns that element
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Returns:
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the topmost item, of arbitrary type
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Raises:
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EmptyError exception if the stack is empty
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'''
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if self.is_empty():
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raise EmptyError("Stack is empty")
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return self._data.remove_head()
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def peek(self) -> T:
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''' returns the topmost element from the stack without modifying the stack
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Returns:
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the topmost item, of arbitrary type
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Raises:
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EmptyError exception if the stack is empty
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'''
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if self.is_empty():
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raise EmptyError("Stack is empty")
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return self._data.get_head()
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def is_empty(self) -> bool:
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''' indicates whether the stack is empty
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Returns:
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True if the stack is empty, False otherwise
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'''
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return len(self._data) == 0
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def __str__(self) -> str:
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''' returns an str implementation of the Stack '''
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return str(self._data)
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def main():
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'''test functions'''
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s = Stack() # I added this so stack doesnt need to be reinitialized for each test
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assert len(s) == 0
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assert s.is_empty() is True
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s.push(10)
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assert len(s) == 1
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assert s.peek() == 10
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s.push(20)
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s.push(30)
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assert len(s) == 3
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assert s.peek() == 30
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assert s.pop() == 30
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assert s.pop() == 20
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assert s.pop() == 10
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assert s.is_empty() is True
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try:
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s.pop()
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assert False
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except EmptyError:
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pass
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try:
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s.peek()
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assert False
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except EmptyError:
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pass
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print("All Stack tests passed.") #only runs if all previous tests pass
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if __name__ == "__main__":
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main()
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