a repo for data-structures assignments for the first half of python 401

Authored by Selena Flannery and Patrick Trompeter

Linked_list: Classic linked list created with no use of python list methods.

Inspired by: https://www.codefellows.org/blog/implementing-a-singly-linked-list-in-python

Stacks: Python Stack with use of Composition from Linked_list

Double Linked List:

Queue:

Selena Parens: A simple module to calculate that all open parens in a string have proper closing one. Returns 0 if all parenthesis have a match. Retuns 1 if there are too many open parens Returns -1 if there are too many closing parens, or if the closing parens are not properly proceeded by an open paren.