{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "collectible-interval",
   "metadata": {},
   "source": [
    "# Python Tip #1: Functions"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "warming-wiring",
   "metadata": {},
   "source": [
    "Functions are separately defined code snippets that you can then use in your main code."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "objective-korean",
   "metadata": {},
   "outputs": [],
   "source": [
    "def double(number): # arguments = input\n",
    "    new_number = 2*number\n",
    "    return new_number"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "metric-monday",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "10"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "double(5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "announced-spokesman",
   "metadata": {},
   "outputs": [],
   "source": [
    "def print_hello():\n",
    "    print(\"hello\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "american-contemporary",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "hello\n"
     ]
    }
   ],
   "source": [
    "print_hello()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "productive-illness",
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "moving-lending",
   "metadata": {},
   "outputs": [],
   "source": [
    "def double(number=7): # number will default to 7 if you don't specify it\n",
    "    new_number = 2*number\n",
    "    return new_number"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "answering-textbook",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "14"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "double()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "id": "assured-regard",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "10"
      ]
     },
     "execution_count": 8,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "double(5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "black-sheet",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "10"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "double(number=5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "id": "continental-delivery",
   "metadata": {},
   "outputs": [],
   "source": [
    "def double(number): # arguments = input\n",
    "    new_number = 2*number\n",
    "    return new_number"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "greater-motel",
   "metadata": {},
   "source": [
    "\"Lambda Functions\" sound very fancy, but they are just a quicker way to define very simple functions."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "serial-explanation",
   "metadata": {},
   "source": [
    "```py\n",
    "double = lambda x : 2*x\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "worth-mystery",
   "metadata": {},
   "source": [
    "`   [name] = lambda [inputs] : [outputs]`"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "id": "allied-matthew",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "10"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "new_double = lambda number : 2*number\n",
    "new_double(5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "id": "together-frederick",
   "metadata": {},
   "outputs": [],
   "source": [
    "# to do a to the power of b in python, the\n",
    "# syntax is a ** b, not a ^ b\n",
    "combine = lambda x, y: 2*x + 3 * y**2"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "id": "bronze-dynamics",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "22"
      ]
     },
     "execution_count": 14,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "combine(5,2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "id": "turkish-diploma",
   "metadata": {},
   "outputs": [],
   "source": [
    "# default argument with a lambda function\n",
    "new_combine = lambda x=1, y=1 : 2*x + 3*y**2"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "id": "8e7d7186",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "22"
      ]
     },
     "execution_count": 30,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "new_combine(5,2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "id": "7ecb8467",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "13"
      ]
     },
     "execution_count": 28,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "new_combine(5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "id": "20fd253a",
   "metadata": {},
   "outputs": [],
   "source": [
    "def example(x, y=3):\n",
    "    return x + y"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "id": "3a603ad3",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "3"
      ]
     },
     "execution_count": 22,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "example(y=1, x=2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "30561ecb",
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "34788319",
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "markdown",
   "id": "subtle-prompt",
   "metadata": {},
   "source": [
    "They are often useful (as we'll see later) for extracting one component of a tuple or list."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "id": "found-minute",
   "metadata": {},
   "outputs": [],
   "source": [
    "second_component = lambda r : r[1]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 32,
   "id": "individual-stevens",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "-8"
      ]
     },
     "execution_count": 32,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "second_component([5, -8, 1])"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "applied-lawrence",
   "metadata": {},
   "source": [
    "This is totally equivalent to:"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "expanded-advice",
   "metadata": {},
   "source": [
    "```py\n",
    "def second_component(r):\n",
    "    return r[1]\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "automated-fitting",
   "metadata": {},
   "source": [
    "This is mostly useful when you just want to use the function in one spot, and not define it forever."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "fancy-edmonton",
   "metadata": {},
   "source": [
    "When sorting a list, you can give it a \"key\" function to tell it what to sort by."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 33,
   "id": "interracial-fifteen",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[-5, 1, 0, 7, -10]\n",
      "[-10, -5, 0, 1, 7]\n"
     ]
    }
   ],
   "source": [
    "L = [-5, 1, 0, 7, -10]\n",
    "print(L)\n",
    "L.sort()\n",
    "print(L)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 34,
   "id": "educated-jurisdiction",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[0, 1, -5, 7, -10]\n"
     ]
    }
   ],
   "source": [
    "# this sorts numbers according to their absolute\n",
    "# value, not the number itself\n",
    "L.sort(key=lambda x : abs(x))\n",
    "print(L)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "useful-container",
   "metadata": {},
   "outputs": [],
   "source": [
    "L"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "pressed-starter",
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "code",
   "execution_count": 36,
   "id": "analyzed-myanmar",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[(0, 3), (-1, 7), (2, 5)]\n"
     ]
    }
   ],
   "source": [
    "L = [(0, 3), (-1, 7), (2, 5)]\n",
    "print(L)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 37,
   "id": "aggressive-experience",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[(-1, 7), (0, 3), (2, 5)]"
      ]
     },
     "execution_count": 37,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sorted(L)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "endless-relation",
   "metadata": {},
   "outputs": [],
   "source": [
    "L"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 38,
   "id": "impaired-rover",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[(0, 3), (2, 5), (-1, 7)]"
      ]
     },
     "execution_count": 38,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sorted(L, key=lambda x : x[1])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 40,
   "id": "communist-occasions",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[(0, 3), (2, 5), (-1, 7)]"
      ]
     },
     "execution_count": 40,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# other version\n",
    "def second_component(x):\n",
    "    return x[1]\n",
    "sorted(L, key=second_component)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 41,
   "id": "592eb824",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[-3, 4, 0]\n",
      "[-3, 0, 4]\n"
     ]
    }
   ],
   "source": [
    "# when you do L.sort(), it sorts the variable in place\n",
    "# when you do sorted(L), it leaves L alone but returns\n",
    "#   a new list that has been sorted\n",
    "L = [-3, 4, 0]\n",
    "R = sorted(L)\n",
    "print(L)\n",
    "print(R)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 42,
   "id": "9087c0d8",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[-3, 0, 4]\n"
     ]
    }
   ],
   "source": [
    "L = [-3, 4, 0]\n",
    "L.sort()\n",
    "print(L)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "5f8b26c1",
   "metadata": {},
   "outputs": [],
   "source": []
  }
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