{
  "cells": [
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "# Python Introduction: Functions"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "Functions help extract out common code blocks.\n",
        "\n",
        "Let's define a function `print_greeting()`."
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 1,
      "metadata": {
        "collapsed": false
      },
      "outputs": [],
      "source": [
        "def print_greeting():\n",
        "    print(\"Hi there, how are you?\")\n",
        "    print(\"Long time no see.\")"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "And call it:"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 2,
      "metadata": {
        "collapsed": false
      },
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "Hi there, how are you?\n",
            "Long time no see.\n"
          ]
        }
      ],
      "source": [
        "print_greeting()"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "That's a bit impersonal."
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 3,
      "metadata": {
        "collapsed": false
      },
      "outputs": [],
      "source": [
        "def print_greeting(name):\n",
        "\n",
        "    print(\"Hi there, {0}, how are you?\".format(name))\n",
        "\n",
        "    print(\"Long time no see.\")"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 4,
      "metadata": {
        "collapsed": false
      },
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "Hi there, Andreas, how are you?\n",
            "Long time no see.\n"
          ]
        }
      ],
      "source": [
        "print_greeting(\"Andreas\")"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "But we might not know their name.\n",
        "\n",
        "(And we just changed the interface of `print_greeting`!)"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 6,
      "metadata": {
        "collapsed": false
      },
      "outputs": [],
      "source": [
        "def print_greeting(name=\"my friend\"):\n",
        "\n",
        "    print(\"Hi there, {0}, how are you?\".format(name))\n",
        "\n",
        "    print(\"Long time no see.\")"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 7,
      "metadata": {
        "collapsed": false
      },
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "Hi there, Andreas, how are you?\n",
            "Long time no see.\n",
            "Hi there, my friend, how are you?\n",
            "Long time no see.\n"
          ]
        }
      ],
      "source": [
        "print_greeting(\"Andreas\")\n",
        "print_greeting()"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "----"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "Function parameters work like variables.\n",
        "\n",
        "So what does this do?"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 8,
      "metadata": {
        "collapsed": false
      },
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "[1, 2, 3, 5]\n"
          ]
        }
      ],
      "source": [
        "def my_func(my_list):\n",
        "    my_list.append(5)\n",
        "    \n",
        "l = [1,2,3]\n",
        "my_func(l)\n",
        "print(l)"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "Can be very surprising!\n",
        "\n",
        "Define a better function `my_func_2`:"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 9,
      "metadata": {
        "collapsed": false
      },
      "outputs": [],
      "source": [
        "def my_func_2(my_list):\n",
        "\n",
        "    return my_list + [5]"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 10,
      "metadata": {
        "collapsed": false
      },
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "[1, 2, 3]\n",
            "[1, 2, 3, 5]\n"
          ]
        }
      ],
      "source": [
        "l = [1,2,3]\n",
        "l2 = my_func_2(l)\n",
        "print(l)\n",
        "print(l2)"
      ]
    }
  ],
  "metadata": {},
  "nbformat": 4,
  "nbformat_minor": 0
}