Initial upload

Author: joeyajames

Python List Iteration.ipynb

@@ -0,0 +1,197 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Python List Iteration\n",
+    "A variety of ways to iterate Lists, including for loop, while loop, enumerate."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "----\n",
+    "The standard for loop works great if inside the loop you only need the item and not its index."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "a\n",
+      "b\n",
+      "c\n",
+      "d\n",
+      "e\n"
+     ]
+    }
+   ],
+   "source": [
+    "letters = ['a', 'b', 'c', 'd', 'e']\n",
+    "\n",
+    "for letter in letters:\n",
+    "    print(letter)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "----\n",
+    "If you need the index inside the loop you can use range(len(list)).  \n",
+    "Then you can always get the list item if needed by using the index."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "letters 0 = a\n",
+      "letters 1 = b\n",
+      "letters 2 = c\n",
+      "letters 3 = d\n",
+      "letters 4 = e\n"
+     ]
+    }
+   ],
+   "source": [
+    "for index in range(len(letters)):\n",
+    "    print('letters', index, '=', letters[index])"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "----\n",
+    "Best option if you need both index and item inside the loop is to use Python's **enumerate** function.  \n",
+    "Enumerate works in both Python 2.x and 3.x"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "letters 0 = a\n",
+      "letters 1 = b\n",
+      "letters 2 = c\n",
+      "letters 3 = d\n",
+      "letters 4 = e\n"
+     ]
+    }
+   ],
+   "source": [
+    "for index, item in enumerate(letters):\n",
+    "    print('letters', index, '=', item)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Enumerate actually returns an iterable enumerate object,  \n",
+    "which is a sequence of tuples of (index, item)."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "(0, 'a')\n",
+      "(1, 'b')\n",
+      "<class 'enumerate'>\n"
+     ]
+    }
+   ],
+   "source": [
+    "enum_obj = enumerate(letters)\n",
+    "print(next(enum_obj))\n",
+    "print(next(enum_obj))\n",
+    "print(type(enum_obj))"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "----\n",
+    "Probably the clumsiest way to iterate a list in Python -- the **while loop**.  \n",
+    "Requires index initialization before list, and incrementation inside loop."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "letters 0 = a\n",
+      "letters 1 = b\n",
+      "letters 2 = c\n",
+      "letters 3 = d\n",
+      "letters 4 = e\n"
+     ]
+    }
+   ],
+   "source": [
+    "index = 0\n",
+    "while index < len(letters): \n",
+    "    print('letters', index, '=', letters[index]) \n",
+    "    index += 1"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.7.0"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}