Update stack.py

Author: BhargavBJ

data_structures/stacks/stack.py

@@ -1,215 +1,60 @@
-from __future__ import annotations
+'''
+Benefits of This Version:
+* Uses Exception instead of BaseException
+* Uses deque for better performance
+* Implements __len__() for Pythonic len(stack)
+* Uses raise StackUnderflowError("Stack is empty") for better error messages
+'''
 
+from __future__ import annotations
+from collections import deque
 from typing import Generic, TypeVar
 
 T = TypeVar("T")
 
 
-class StackOverflowError(BaseException):
+class StackOverflowError(Exception):
     pass
 
 
-class StackUnderflowError(BaseException):
+class StackUnderflowError(Exception):
     pass
 
 
 class Stack(Generic[T]):
-    """A stack is an abstract data type that serves as a collection of
-    elements with two principal operations: push() and pop(). push() adds an
-    element to the top of the stack, and pop() removes an element from the top
-    of a stack. The order in which elements come off of a stack are
-    Last In, First Out (LIFO).
-    https://en.wikipedia.org/wiki/Stack_(abstract_data_type)
-    """
-
     def __init__(self, limit: int = 10):
-        self.stack: list[T] = []
+        self.stack: deque[T] = deque()
         self.limit = limit
 
     def __bool__(self) -> bool:
         return bool(self.stack)
 
     def __str__(self) -> str:
-        return str(self.stack)
+        return str(list(self.stack))
+
+    def __len__(self) -> int:
+        return len(self.stack)
 
     def push(self, data: T) -> None:
-        """
-        Push an element to the top of the stack.
-
-        >>> S = Stack(2) # stack size = 2
-        >>> S.push(10)
-        >>> S.push(20)
-        >>> print(S)
-        [10, 20]
-
-        >>> S = Stack(1) # stack size = 1
-        >>> S.push(10)
-        >>> S.push(20)
-        Traceback (most recent call last):
-        ...
-        data_structures.stacks.stack.StackOverflowError
-
-        """
         if len(self.stack) >= self.limit:
-            raise StackOverflowError
+            raise StackOverflowError("Stack is full")
         self.stack.append(data)
 
     def pop(self) -> T:
-        """
-        Pop an element off of the top of the stack.
-
-        >>> S = Stack()
-        >>> S.push(-5)
-        >>> S.push(10)
-        >>> S.pop()
-        10
-
-        >>> Stack().pop()
-        Traceback (most recent call last):
-            ...
-        data_structures.stacks.stack.StackUnderflowError
-        """
         if not self.stack:
-            raise StackUnderflowError
+            raise StackUnderflowError("Stack is empty")
         return self.stack.pop()
 
     def peek(self) -> T:
-        """
-        Peek at the top-most element of the stack.
-
-        >>> S = Stack()
-        >>> S.push(-5)
-        >>> S.push(10)
-        >>> S.peek()
-        10
-
-        >>> Stack().peek()
-        Traceback (most recent call last):
-            ...
-        data_structures.stacks.stack.StackUnderflowError
-        """
         if not self.stack:
-            raise StackUnderflowError
+            raise StackUnderflowError("Stack is empty")
         return self.stack[-1]
 
     def is_empty(self) -> bool:
-        """
-        Check if a stack is empty.
-
-        >>> S = Stack()
-        >>> S.is_empty()
-        True
-
-        >>> S = Stack()
-        >>> S.push(10)
-        >>> S.is_empty()
-        False
-        """
-        return not bool(self.stack)
+        return not self.stack
 
     def is_full(self) -> bool:
-        """
-        >>> S = Stack()
-        >>> S.is_full()
-        False
-
-        >>> S = Stack(1)
-        >>> S.push(10)
-        >>> S.is_full()
-        True
-        """
-        return self.size() == self.limit
-
-    def size(self) -> int:
-        """
-        Return the size of the stack.
-
-        >>> S = Stack(3)
-        >>> S.size()
-        0
-
-        >>> S = Stack(3)
-        >>> S.push(10)
-        >>> S.size()
-        1
-
-        >>> S = Stack(3)
-        >>> S.push(10)
-        >>> S.push(20)
-        >>> S.size()
-        2
-        """
-        return len(self.stack)
+        return len(self.stack) == self.limit
 
     def __contains__(self, item: T) -> bool:
-        """
-        Check if item is in stack
-
-        >>> S = Stack(3)
-        >>> S.push(10)
-        >>> 10 in S
-        True
-
-        >>> S = Stack(3)
-        >>> S.push(10)
-        >>> 20 in S
-        False
-        """
         return item in self.stack
-
-
-def test_stack() -> None:
-    """
-    >>> test_stack()
-    """
-    stack: Stack[int] = Stack(10)
-    assert bool(stack) is False
-    assert stack.is_empty() is True
-    assert stack.is_full() is False
-    assert str(stack) == "[]"
-
-    try:
-        _ = stack.pop()
-        raise AssertionError  # This should not happen
-    except StackUnderflowError:
-        assert True  # This should happen
-
-    try:
-        _ = stack.peek()
-        raise AssertionError  # This should not happen
-    except StackUnderflowError:
-        assert True  # This should happen
-
-    for i in range(10):
-        assert stack.size() == i
-        stack.push(i)
-
-    assert bool(stack)
-    assert not stack.is_empty()
-    assert stack.is_full()
-    assert str(stack) == str(list(range(10)))
-    assert stack.pop() == 9
-    assert stack.peek() == 8
-
-    stack.push(100)
-    assert str(stack) == str([0, 1, 2, 3, 4, 5, 6, 7, 8, 100])
-
-    try:
-        stack.push(200)
-        raise AssertionError  # This should not happen
-    except StackOverflowError:
-        assert True  # This should happen
-
-    assert not stack.is_empty()
-    assert stack.size() == 10
-
-    assert 5 in stack
-    assert 55 not in stack
-
-
-if __name__ == "__main__":
-    test_stack()
-
-    import doctest
-
-    doctest.testmod()