Restructured packages.

stacks_queues/stack/stack.py

@@ -0,0 +1,29 @@
+
+class Node(object):
+    def __init__(self, data):
+        self.data = data
+        self.next = None
+
+class Stack(object):
+    def __init__(self, top=None):
+        self.top = top
+
+    def push(self, data):
+        node = Node(data)
+        node.next = self.top
+        self.top = node
+
+    def pop(self):
+        if self.top is not None:
+            data = self.top.data
+            self.top = self.top.next
+            return data
+        return None
+
+    def peek(self):
+        if self.top is not None:
+            return self.top.data
+        return None
+
+    def is_empty(self):
+        return self.peek() is None