From 7a166bed6700bfce4ed60cc9ff6925ef53860374 Mon Sep 17 00:00:00 2001
From: Donne Martin <donne.martin@gmail.com>
Date: Sat, 20 Feb 2016 08:11:49 -0500
Subject: [PATCH] Polish stack solution.

---
 stacks_queues/stack/stack.py             | 21 +++++++---------
 stacks_queues/stack/stack_solution.ipynb | 31 +++++++++++-------------
 2 files changed, 23 insertions(+), 29 deletions(-)

diff --git a/stacks_queues/stack/stack.py b/stacks_queues/stack/stack.py
index 27dceed..b9357f7 100644
--- a/stacks_queues/stack/stack.py
+++ b/stacks_queues/stack/stack.py
@@ -1,8 +1,8 @@
 class Node(object):
 
-    def __init__(self, data):
+    def __init__(self, data, next=None):
         self.data = data
-        self.next = None
+        self.next = next
 
 
 class Stack(object):
@@ -11,21 +11,18 @@ class Stack(object):
         self.top = top
 
     def push(self, data):
-        node = Node(data)
-        node.next = self.top
+        node = Node(data, 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
+        if self.top is None:
+            return None
+        data = self.top.data
+        self.top = self.top.next
+        return data
 
     def peek(self):
-        if self.top is not None:
-            return self.top.data
-        return None
+        return self.top.data if self.top is not None else None
 
     def is_empty(self):
         return self.peek() is None
\ No newline at end of file
diff --git a/stacks_queues/stack/stack_solution.ipynb b/stacks_queues/stack/stack_solution.ipynb
index a05fef9..d3896ce 100644
--- a/stacks_queues/stack/stack_solution.ipynb
+++ b/stacks_queues/stack/stack_solution.ipynb
@@ -137,9 +137,9 @@
     "%%writefile stack.py\n",
     "class Node(object):\n",
     "\n",
-    "    def __init__(self, data):\n",
+    "    def __init__(self, data, next=None):\n",
     "        self.data = data\n",
-    "        self.next = None\n",
+    "        self.next = next\n",
     "\n",
     "\n",
     "class Stack(object):\n",
@@ -148,21 +148,18 @@
     "        self.top = top\n",
     "\n",
     "    def push(self, data):\n",
-    "        node = Node(data)\n",
-    "        node.next = self.top\n",
+    "        node = Node(data, self.top)\n",
     "        self.top = node\n",
     "\n",
     "    def pop(self):\n",
-    "        if self.top is not None:\n",
-    "            data = self.top.data\n",
-    "            self.top = self.top.next\n",
-    "            return data\n",
-    "        return None\n",
+    "        if self.top is None:\n",
+    "            return None\n",
+    "        data = self.top.data\n",
+    "        self.top = self.top.next\n",
+    "        return data\n",
     "\n",
     "    def peek(self):\n",
-    "        if self.top is not None:\n",
-    "            return self.top.data\n",
-    "        return None\n",
+    "        return self.top.data if self.top is not None else None\n",
     "\n",
     "    def is_empty(self):\n",
     "        return self.peek() is None"
@@ -308,21 +305,21 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 2",
+   "display_name": "Python 3",
    "language": "python",
-   "name": "python2"
+   "name": "python3"
   },
   "language_info": {
    "codemirror_mode": {
     "name": "ipython",
-    "version": 2
+    "version": 3
    },
    "file_extension": ".py",
    "mimetype": "text/x-python",
    "name": "python",
    "nbconvert_exporter": "python",
-   "pygments_lexer": "ipython2",
-   "version": "2.7.10"
+   "pygments_lexer": "ipython3",
+   "version": "3.4.3"
   }
  },
  "nbformat": 4,