{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "VcybRL6lIq-O"
   },
   "source": [
    "# Loops and Conditionals"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "fxa7FGu7Iq-Q"
   },
   "source": [
    "## For Loops\n",
    "\n",
    "A for loop is used for iterating over a sequence. The sequence can be a list, a tuple, a dictionary, a set, or a string.\n",
    "\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "id": "FD8RTQabIq-R"
   },
   "outputs": [],
   "source": [
    "cities = ['San Francisco', 'Los Angeles', 'New York', 'Atlanta']\n",
    "\n",
    "for city in cities:\n",
    "    print(city)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "CtTpoZsiIq-S"
   },
   "source": [
    "To iterate over a dictionary, you can call the `items()` method on it which returns a tuple of key and value for each item."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "id": "IhyJMlyYIq-S"
   },
   "outputs": [],
   "source": [
    "data = {'city': 'San Francisco', 'population': 881549, 'coordinates': (-122.4194, 37.7749) }\n",
    "\n",
    "for x, y in data.items():\n",
    "    print(x, y)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "MC-cZ4jTIq-S"
   },
   "source": [
    "The built-in `range()` function allows you to create sequence of numbers that you can iterate over"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "id": "s5aQD5EoIq-S"
   },
   "outputs": [],
   "source": [
    "for x in range(5):\n",
    "    print(x)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "-EdoGJ_NIq-S"
   },
   "source": [
    "The range function can also take a start and an end number"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "id": "mt9ist7mIq-T"
   },
   "outputs": [],
   "source": [
    "for x in range(1, 10, 2):\n",
    "    print(x)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "YjmjJ0_RIq-T"
   },
   "source": [
    "## Conditionals\n",
    "\n",
    "Python supports logical conditions such as equals, not equals, greater than etc. These conditions can be used in several ways, most commonly in *if statements* and loops.\n",
    "\n",
    "An *if statement* is written by using the `if` keyword.\n",
    "\n",
    "Note: A very common error that programmers make is to use *=* to evaluate a *equals to* condition. The *=* in Python means assignment, not equals to. Always ensure that you use the *==* for an equals to condition."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "id": "ZXzXSg5pIq-T"
   },
   "outputs": [],
   "source": [
    "for city in cities:\n",
    "    if city == 'Atlanta':\n",
    "        print(city)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "RDVjqgLSIq-T"
   },
   "source": [
    "You can use `else` keywords along with `if` to match elements that do not meet the condition"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "id": "UVprKXleIq-T"
   },
   "outputs": [],
   "source": [
    "for city in cities:\n",
    "    if city == 'Atlanta':\n",
    "        print(city)\n",
    "    else:\n",
    "        print('This is not Atlanta')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "AgyTuBC5Iq-T"
   },
   "source": [
    "Python relies on indentation (whitespace at the beginning of a line) to define scope in the for loop and if statements. So make sure your code is properly indented."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "EyuMTS1EIq-U"
   },
   "source": [
    "You can evaluate a series of conditions using the `elif` keyword.\n",
    "\n",
    "Multiple criteria can be combined using the `and` and `or` keywords."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "id": "ieLSAlWWIq-U"
   },
   "outputs": [],
   "source": [
    "cities_population = {\n",
    "    'San Francisco': 881549,\n",
    "    'Los Angeles': 3792621,\n",
    "    'New York': 8175133,\n",
    "    'Atlanta':498044\n",
    "}\n",
    "\n",
    "for city, population in cities_population.items():\n",
    "    if population < 1000000:\n",
    "        print('{} is a small city'.format(city))\n",
    "    elif population > 1000000 and population < 5000000:\n",
    "        print('{} is a big city'.format(city))\n",
    "    else:\n",
    "        print('{} is a mega city'.format(city))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "wjkvlcskIq-U"
   },
   "source": [
    "## Control Statements\n",
    "\n",
    "A for-loop iterates over each item in the sequence. Sometimes is desirable to stop the execution, or skip certain parts of the for-loops. Python has special statements, `break`, `continue` and `pass`."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "nVioGPW_Iq-U"
   },
   "source": [
    "A `break` statement will stop the loop and exit out of it"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "id": "0RbsWzSoIq-U"
   },
   "outputs": [],
   "source": [
    "for city in cities:\n",
    "    print(city)\n",
    "    if city == 'Los Angeles':\n",
    "        print('I found Los Angeles')\n",
    "        break"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "zKbhSW6SIq-U"
   },
   "source": [
    "A `continue` statement will skip the remaining part of the loop and go to the next iteration"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "id": "5Pp2J0KdIq-U"
   },
   "outputs": [],
   "source": [
    "for city in cities:\n",
    "    if city == 'Los Angeles':\n",
    "        continue\n",
    "    print(city)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "oyk8QjIhIq-U"
   },
   "source": [
    "A `pass` statement doesn't do anything. It is useful when some code is required to complete the syntax, but you do not want any code to execute. It is typically used as a placeholder when a function is not complete."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "id": "yX5rjvV6Iq-U"
   },
   "outputs": [],
   "source": [
    "for city in cities:\n",
    "    if city == 'Los Angeles':\n",
    "        pass\n",
    "    else:\n",
    "        print(city)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "lEPeBA-MIq-U"
   },
   "source": [
    "## Exercise\n",
    "\n",
    "The Fizz Buzz challenge.\n",
    "\n",
    "Write a program that prints the numbers from 1 to 100 and for multiples of 3 print **Fizz** instead of the number and for the multiples of 5 print **Buzz**. If it is divisible by both, print **FizzBuzz**.\n",
    "\n",
    "So the output should be something like below\n",
    "\n",
    "`1, 2, Fizz, 4, Buzz, Fizz ... 13, 14, FizzBuzz, ...`\n",
    "\n",
    "Breaking down the problem further, we need to create for-loop with following conditions\n",
    "\n",
    "- If the number is a multiple of both 3 and 5 (i.e. 15), print FizzBuzz\n",
    "- If the number is multiple of 3, print Fizz\n",
    "- If the number is multiple of 5, print Buzz\n",
    "- Otherwise print the number\n",
    "\n",
    "Hint: See the code cell below. Use the modulus operator **%** to check if a number is divisible by another. `10 % 5` equals 0, meaning it is divisible by 5.\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "id": "KseRBGB2Iq-U"
   },
   "outputs": [],
   "source": [
    "for x in range(1, 10):\n",
    "    if x%2 == 0:\n",
    "        print('{} is divisible by 2'.format(x))\n",
    "    else:\n",
    "        print('{} is not divisible by 2'.format(x))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "id": "TPC6zR-BIq-U"
   },
   "source": [
    "----"
   ]
  }
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