added module for simple cs structures

pmkoalas/_struct/__init__.py

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+from pmkoalas._struct.collections import *

pmkoalas/_struct/collections.py

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+'''
+This module contains typical useful restricts on collections in computer 
+science.
+
+Included are the following structures:
+    - `Stack`
+'''
+from copy import deepcopy
+from typing import Collection, Union
+
+class Stack():
+    '''
+    A structure to represent a stack, where you can push, peek, or pop 
+    elements on the stack.
+    '''
+
+    def __init__(self, starting:Collection) -> None:
+        '''
+        Initializes the stack with the starting collection, where the last
+        element of the starting collection is at the top of the stack.
+        '''
+        self._stack = []
+        for e in starting:
+            self.push(e)
+
+    def push(self, element) -> None:
+        '''
+        Pushes a copy of the element onto the stack.
+        '''
+        self._stack.append(deepcopy(element))
+
+    def pop(self) -> Union[None, object]:
+        '''
+        Pop the top element off the stack, or return None when empty.
+        '''
+        if (len(self._stack) == 0):
+            return None
+        return self._stack.pop()
+
+    def peek(self) -> Union[None, object]:
+        '''
+        Peek at the top element of the stack or returns None when empty.
+        Returns a copy of the element.
+        '''
+        if (len(self._stack) == 0):
+            return None
+        return deepcopy(self._stack[-1])
+
+    def is_empty(self) -> bool:
+        '''
+        Returns True if the stack is empty, False otherwise.
+        '''
+        return len(self._stack) == 0