stack.py: Add Stack Data Structure

This adds Stack data structure in Python Language.
Includes basic functionality of stack (push, pop, top, display).

Closes #37

README.md

@@ -27,7 +27,7 @@ This repository contains examples of various algorithms written on different pro
 | Data Structure                                                                                  | C                                     | CPP                                   | Java                                  | Python                                |
 |:----------------------------------------------------------------------------------------------- |:-------------------------------------:|:-------------------------------------:|:-------------------------------------:|:-------------------------------------:|
 | [Queue](https://en.wikipedia.org/wiki/Queue_(abstract_data_type))                               |                                       | [:octocat:](queue/Cpp)                |                                       |                                       |
-| [Stack](https://en.wikipedia.org/wiki/Stack_(abstract_data_type))                               |                                       |                                       | [:octocat:](stack/Java)               |                                       |
+| [Stack](https://en.wikipedia.org/wiki/Stack_(abstract_data_type))                               |                                       |                                       | [:octocat:](stack/Java)               | [:octocat:](stack/Python)             |
 | [Linear Linked List](https://en.wikipedia.org/wiki/Linked_list)                                 | [:octocat:](linked_list/C)            |                                       |                                       |                                       |
 | [AVL Tree](https://en.wikipedia.org/wiki/AVL_tree)                                              |                                       |                                       | [:octocat:](avl_tree/Java)            |                                       |
 

stack/Python/stack.py

@@ -0,0 +1,63 @@
+class Stack:
+    """
+    Class for operations related to stack.
+    """
+
+    def __init__(self):
+
+        self.stack = []  # Initialise empty stack
+
+    def push(self, dataval):
+        """
+        Method to push items in stack.
+
+        :param dataval: Value that user needs to push.
+        """
+
+        self.stack.append(dataval)
+
+    def pop(self):
+        """
+        Method for removing the last element from the stack.
+
+        :return:   Element that is popped.
+        """
+
+        if len(self.stack) <= 0:
+            # Raise an error if stack is empty.
+            return "No element in the Stack"
+
+        else:
+            return self.stack.pop()
+
+    def top(self):
+        """
+        Method to show the last element of the stack.
+
+        :return:    last element of the stack.
+        """
+
+        return self.stack[len(self.stack)-1]
+
+    def display(self):
+        """
+        Method to print all elements of the stack.
+        """
+
+        print(*self.stack)
+
+
+def main():
+    AStack = Stack()
+    AStack.push("Mon")
+    AStack.push("Tue")
+    AStack.pop()
+    AStack.push("Wed")
+    m = AStack.top()
+    print(m)
+    AStack.push("Thu")
+    AStack.display()
+
+
+if __name__ == "__main__":
+    main()