{
 "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 well if it is used 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": []
  }
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