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[mypy] Fix type annotations for stack_using_dll.py (#5577)

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* Fix mypy annotations for stack_using_dll.py

* Replace Optional with inline union type
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Edward Nuno 2021-10-26 12:12:46 -07:00 committed by GitHub
parent c0ed031b3f
commit 9a03919052
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1 changed files with 24 additions and 16 deletions
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40
data_structures/stacks/stack_using_dll.py
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@ -1,15 +1,21 @@
# A complete working Python program to demonstrate all # A complete working Python program to demonstrate all
# stack operations using a doubly linked list # stack operations using a doubly linked list
from __future__ import annotations
class Node: from typing import Generic, TypeVar
def __init__(self, data):
T = TypeVar("T")
class Node(Generic[T]):
def __init__(self, data: T):
self.data = data # Assign data self.data = data # Assign data
self.next = None # Initialize next as null self.next: Node[T] | None = None # Initialize next as null
self.prev = None # Initialize prev as null self.prev: Node[T] | None = None # Initialize prev as null
class Stack: class Stack(Generic[T]):
""" """
>>> stack = Stack() >>> stack = Stack()
>>> stack.is_empty() >>> stack.is_empty()
@ -35,10 +41,10 @@ class Stack:
2->1->0-> 2->1->0->
""" """
def __init__(self): def __init__(self) -> None:
self.head = None self.head: Node[T] | None = None
def push(self, data): def push(self, data: T) -> None:
"""add a Node to the stack""" """add a Node to the stack"""
if self.head is None: if self.head is None:
self.head = Node(data) self.head = Node(data)
@ -49,21 +55,23 @@ class Stack:
new_node.prev = None new_node.prev = None
self.head = new_node self.head = new_node
def pop(self): def pop(self) -> T | None:
"""pop the top element off the stack""" """pop the top element off the stack"""
if self.head is None: if self.head is None:
return None return None
else: else:
assert self.head is not None
temp = self.head.data temp = self.head.data
self.head = self.head.next self.head = self.head.next
self.head.prev = None if self.head is not None:
self.head.prev = None
return temp return temp
def top(self): def top(self) -> T | None:
"""return the top element of the stack""" """return the top element of the stack"""
return self.head.data return self.head.data if self.head is not None else None
def __len__(self): def __len__(self) -> int:
temp = self.head temp = self.head
count = 0 count = 0
while temp is not None: while temp is not None:
@ -71,10 +79,10 @@ class Stack:
temp = temp.next temp = temp.next
return count return count
def is_empty(self): def is_empty(self) -> bool:
return self.head is None return self.head is None
def print_stack(self): def print_stack(self) -> None:
print("stack elements are:") print("stack elements are:")
temp = self.head temp = self.head
while temp is not None: while temp is not None:
@ -86,7 +94,7 @@ class Stack:
if __name__ == "__main__": if __name__ == "__main__":
# Start with the empty stack # Start with the empty stack
stack = Stack() stack: Stack[int] = Stack()
# Insert 4 at the beginning. So stack becomes 4->None # Insert 4 at the beginning. So stack becomes 4->None
print("Stack operations using Doubly LinkedList") print("Stack operations using Doubly LinkedList")