Frank's lesson material

Day2_AM1/old/Functions modules and all that....ipynb

+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {
+    "collapsed": true
+   },
+   "source": [
+    "# Functions, Modules and all that...\n",
+    "We have already used plenty of functions in python yesterday, now it's time to define our own and see how we can work with functions in Python."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "# The syntax of function definitions in python:\n",
+    "def fahrenheit_to_kelvin(temperature, verbose=False):\n",
+    "    temp_in_kelvin = (temperature - 32) * 5/9 + 273.15\n",
+    "    if verbose:\n",
+    "        print(f\"The temperature {temperature}F equals {temp_in_kelvin:0.5}K.\")\n",
+    "        # print(\"The temperature {}F equals {}K.\".format(temperature, temp_in_kelvin))\n",
+    "    return temp_in_kelvin"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The temperature 30F equals 272.04K.\n"
+     ]
+    },
+    {
+     "data": {
+      "text/plain": [
+       "272.0388888888889"
+      ]
+     },
+     "execution_count": 2,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "fahrenheit_to_kelvin(30, verbose=True)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "272.0388888888889"
+      ]
+     },
+     "execution_count": 3,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "fahrenheit_to_kelvin(30)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The temperature 30F equals 272.04K.\n"
+     ]
+    },
+    {
+     "data": {
+      "text/plain": [
+       "272.0388888888889"
+      ]
+     },
+     "execution_count": 4,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "fahrenheit_to_kelvin(30, True)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "# Arguments are identified either by position or by keyword. All positional arguments come before all keyword arguments.\n",
+    "def the_count(one, two, three, four=4, five=5, six=6):\n",
+    "    print(f\"One  : {one}\")\n",
+    "    print(f\"Two  : {two}\")\n",
+    "    print(f\"Three: {three}\")\n",
+    "    print(f\"Four : {four}\")\n",
+    "    print(f\"Five : {five}\")\n",
+    "    print(f\"Six  : {six}\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "ename": "TypeError",
+     "evalue": "the_count() got multiple values for argument 'four'",
+     "output_type": "error",
+     "traceback": [
+      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
+      "\u001b[0;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
+      "\u001b[0;32m<ipython-input-6-29bc3fadc58a>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mthe_count\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;36m10\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;36m2\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;36m3\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;36m4\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0mfour\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0;36m5\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0msix\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0;36m30\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+      "\u001b[0;31mTypeError\u001b[0m: the_count() got multiple values for argument 'four'"
+     ]
+    }
+   ],
+   "source": [
+    "the_count(10,2,3,4,four=5,six=30)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Python 3 5/9 == 0.556\n",
+      "Python 3 5//9 == 0\n",
+      "Python 2 5/9 == 0\n"
+     ]
+    }
+   ],
+   "source": [
+    "# An aside on integer division, in python 2 integer division worked \n",
+    "# differently. It always rounded down to the nearest integer.\n",
+    "# The Python 2 behavior can still be accessed via double slash:\n",
+    "print(f\"Python 3 5/9 == {5/9:0.3}\")\n",
+    "print(f\"Python 3 5//9 == {5//9}\")\n",
+    "print(f\"Python 2 5/9 == {5//9}\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "def kelvin_to_celsius(temperature):\n",
+    "    return temperature - 273.15"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "# Using functions we have defined in new functions works as expected:\n",
+    "def fahrenheit_to_celsius(temperature):\n",
+    "    temp_in_kelvin = fahrenheit_to_kelvin(temperature)\n",
+    "    return kelvin_to_celsius(temp_in_kelvin)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 10,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "-6.666666666666686"
+      ]
+     },
+     "execution_count": 10,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "fahrenheit_to_celsius(20)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 11,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "# So this all works, but \n",
+    "# clearly our functions aren't really specific to our notebook.\n",
+    "# They are quite general. This is why we will now look into moving\n",
+    "# them into their own file. Look at Modular temperatures.ipynb.\n",
+    "\n",
+    "\n",
+    "# A general note: Minimize state, avoid (nested) ifs.\n",
+    "# State makes it hard to understand what your code will do.\n",
+    "# Nested ifs will make it hard to reason about your code.\n",
+    "# Functions are nice to reason about if you don't use globals:\n",
+    "# You can see all their inputs and outputs."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Functional stuff\n",
+    "* you can work with functions as with variables\n",
+    "* you can pass functions as parameters\n",
+    "* you can define functions in functions and return them\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 12,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "f2c = fahrenheit_to_celsius"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 13,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "-6.666666666666686"
+      ]
+     },
+     "execution_count": 13,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "f2c(20)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 14,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "def convert_many(function, temperatures):\n",
+    "    result = list()\n",
+    "    for t in temperatures:\n",
+    "        result.append(function(t))\n",
+    "    return result"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 15,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "[-12.222222222222229, -5.0, 4.444444444444457, -23.333333333333343]\n",
+      "[-12.222222222222229, -5.0, 4.444444444444457, -23.333333333333343]\n"
+     ]
+    }
+   ],
+   "source": [
+    "temp_record_fahr = [10., 23., 40., -10.]\n",
+    "print(convert_many(f2c, temp_record_fahr))\n",
+    "print(list(map(f2c, temp_record_fahr)))"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 16,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "# Why is map wrapped in list? Because by default it returns an iterator.\n",
+    "# The functions are not evaluated until needed:\n",
+    "\n",
+    "l = map(print, temp_record_fahr)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 17,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "10.0\n"
+     ]
+    }
+   ],
+   "source": [
+    "next(l)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 18,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "23.0\n"
+     ]
+    }
+   ],
+   "source": [
+    "next(l)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 19,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "40.0\n"
+     ]
+    }
+   ],
+   "source": [
+    "next(l)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 20,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "-10.0\n"
+     ]
+    }
+   ],
+   "source": [
+    "next(l)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 21,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "ename": "StopIteration",
+     "evalue": "",
+     "output_type": "error",
+     "traceback": [
+      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
+      "\u001b[0;31mStopIteration\u001b[0m                             Traceback (most recent call last)",
+      "\u001b[0;32m<ipython-input-21-101c36968c6d>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mnext\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0ml\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+      "\u001b[0;31mStopIteration\u001b[0m: "
+     ]
+    }
+   ],
+   "source": [
+    "next(l)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 22,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "9000.0"
+      ]
+     },
+     "execution_count": 22,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "def make_me_a_temp_scale(abs_zero):\n",
+    "    \n",
+    "    def celsius_to_frank(temperature):\n",
+    "        return temperature + 273.15 + abs_zero\n",
+    "    \n",
+    "    return celsius_to_frank\n",
+    "\n",
+    "celsius_to_frank_9000 = make_me_a_temp_scale(9000)\n",
+    "celsius_to_frank_9000(-273.15)\n",
+    "\n",
+    "# In this temperature scale, all temperatures are over 9000."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 23,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "# We can do both!\n",
+    "\n",
+    "def make_verbose(function):\n",
+    "    def f2(arg):\n",
+    "        res = function(arg)\n",
+    "        print(f\"Function {function.__name__} returned {res}\")\n",
+    "        return res\n",
+    "    return f2\n",
+    "\n",
+    "# Of course this won't work if the function has more than one argument.\n",
+    "# To see how to make that work look up *args, and **kwargs."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 24,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "f2c_verbose = make_verbose(f2c)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 25,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Function fahrenheit_to_celsius returned -6.666666666666686\n"
+     ]
+    },
+    {
+     "data": {
+      "text/plain": [
+       "-6.666666666666686"
+      ]
+     },
+     "execution_count": 25,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "f2c_verbose(20)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 26,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "t = (1,2,3)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 27,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "# There is a special syntax for such functions that modify functions,\n",
+    "# they are called function decorators in python and can be used like so:\n",
+    "\n",
+    "@make_verbose\n",
+    "def add_5(x):\n",
+    "    return x+5"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 28,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Function add_5 returned 15\n"
+     ]
+    },
+    {
+     "data": {
+      "text/plain": [
+       "15"
+      ]
+     },
+     "execution_count": 28,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "add_5(10)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 29,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "0\n",
+      "0\n",
+      "0\n",
+      "0\n",
+      "0\n"
+     ]
+    }
+   ],
+   "source": [
+    "# When are default parameters evaluated?\n",
+    "\n",
+    "i=0\n",
+    "\n",
+    "def print_i(x=i):\n",
+    "    print(x)\n",
+    "    \n",
+    "for j in range(5):\n",
+    "    i += 1\n",
+    "    print_i()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 30,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [