Create Stack_Linked_List.py

Author: ashwek

Data_Structure/src/Stack_Linked_List.py

@@ -0,0 +1,62 @@
+class Node:         # Class to create Nodes
+    def __init__(self, Value, Next=None):
+        self.value = Value      # value in Node
+        self.next = Next        # points to next node
+
+class Stack_LL:
+    def __init__(self):
+        self.__top = None       # initially top = None
+        self.__len = 0          # initially length of stack = 0
+
+    def is_empty(self):
+        return self.__top == None
+
+    def push(self, value):
+        self.__top = Node(value, self.__top)        # Create Node with value = "value" & next = "top". Make new node as top
+        self.__len += 1         # increment length
+
+    def pop(self):
+        if(self.is_empty()): raise IndexError("Stack is Empty")         # check if stack is empty
+        else:
+            temp = self.__top               # temp = top
+            self.__top = self.__top.next    # top = next element
+            temp.next = None                # (previous top) temp.next -> None (break the link)
+            self.__len -= 1                 # decrement length
+            return temp.value               # return poped value
+
+    def __len__(self):
+        return self.__len
+
+    def __str__(self):          # return str form of linked list i.e., val1 -> val2 -> None
+        temp = self.__top
+        Values = []
+        while temp:
+            Values.append(str(temp.value))      # add values to "Values"
+            temp = temp.next
+        Values.append("None")
+        return " -> ".join(Values)          # return all Values as string
+
+    # __next__ and __iter__ methods are used to iterate through the object
+
+    # __next__ is used to get the next element in the iterable object
+    def __next__(self):
+        temp = self.__i
+        if (temp == None): raise StopIteration() # if temp = None, temp has reached the end, raise StopIteration to stop iteration
+        self.__i = self.__i.next
+        return temp.value
+
+    # __iter__ returns an iterable object (self) & sets i = top, to iterate through top to end
+    def __iter__(self):
+        self.__i = self.__top
+        return self
+
+if __name__ == '__main__':
+    S1 = Stack_LL()
+
+    for i in range(5, 21, 5):
+        print("push", i, "to stack")
+        S1.push(i)
+
+    print("\nStack : ", S1)
+
+    print("\nPop stack, popped value = ", S1.pop())