Forkwell - 2021-July-6.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Python exercises!\n",
    "\n",
    "With: Reuven M. Lerner, reuven@lerner.co.il\n",
    "- Twitter: @reuvenmlerner\n",
    "- Web: https://lerner.co.il\n",
    "\n",
    "Watch along with me at: https://github.com/reuven/Forkwell-2021-July-6"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Exercises:\n",
    "\n",
    "1. XML creator\n",
    "2. `read_n`\n",
    "3. `once_per_minute`"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# XML creator\n",
    "\n",
    "Problem: Write a function, `xml`, that will take several types of arguments:\n",
    "\n",
    "- tag name (mandatory)\n",
    "- text (optional)\n",
    "- optional keyword arguments that will be used as the attributes\n",
    "\n",
    "The function should return a string containing the XML.\n",
    "\n",
    "Example:\n",
    "\n",
    "```python\n",
    "xml('tagname', 'text', a=1, b=2, c=3)\n",
    "```\n",
    "\n",
    "We would get back:\n",
    "\n",
    "    <tagname a=1 b=2 c=3>text</tagname>\n",
    "    \n",
    "    "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "<mytag></mytag>\n",
      "<mytag>mytext</mytag>\n",
      "<a><b><c>hello</c></b></a>\n",
      "<mytag x=\"100\" y=\"200\" c=\"300\">mytext</mytag>\n"
     ]
    }
   ],
   "source": [
    "def xml(tagname, text='', **kwargs):\n",
    "    attributes = ''\n",
    "    for key, value in kwargs.items():\n",
    "        attributes += f' {key}=\"{value}\"'\n",
    "\n",
    "    return f'<{tagname}{attributes}>{text}</{tagname}>'\n",
    "\n",
    "print(xml('mytag'))\n",
    "print(xml('mytag', 'mytext'))\n",
    "print(xml('a', xml('b', xml('c', 'hello'))))\n",
    "print(xml('mytag', 'mytext', x=100, y=200, c=300))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Exercise: `read_n`\n",
    "\n",
    "When we iterate over a file-like object, each iteration returns the next line in the file. (When we reach the end of the file, the iterations stop.) What if the file we want to read from contains data that's structured in 2-line segments? Or 4-line segments?\n",
    "\n",
    "Write a function, `read_n`, that takes two arguments:\n",
    "\n",
    "- `filename`, the name of the file to read from\n",
    "- `n`, the number of lines that we should get in each chunk\n",
    "\n",
    "This should be a *generator function*, so that we can iterate over it.\n",
    "\n",
    "When we reach the end of the file, we can return fewer than `n` lines, the remainder that's left."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "collapsed": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "##\n",
      "# User Database\n",
      "# \n",
      "# Note that this file is consulted directly only when the system is running\n",
      "# in single-user mode.  At other times this information is provided by\n",
      "# Open Directory.\n",
      "#\n",
      "\n",
      "# See the opendirectoryd(8) man page for additional information about\n",
      "# Open Directory.\n",
      "##\n",
      "nobody:*:-2:-2:Unprivileged User:/var/empty:/usr/bin/false\n",
      "root:*:0:0:System Administrator:/var/root:/bin/sh\n",
      "daemon:*:1:1:System Services:/var/root:/usr/bin/false\n",
      "_uucp:*:4:4:Unix to Unix Copy Protocol:/var/spool/uucp:/usr/sbin/uucico\n",
      "\n",
      "_taskgated:*:13:13:Task Gate Daemon:/var/empty:/usr/bin/false\n",
      "_networkd:*:24:24:Network Services:/var/networkd:/usr/bin/false\n",
      "_installassistant:*:25:25:Install Assistant:/var/empty:/usr/bin/false\n",
      "_lp:*:26:26:Printing Services:/var/spool/cups:/usr/bin/false\n",
      "_postfix:*:27:27:Postfix Mail Server:/var/spool/postfix:/usr/bin/false\n",
      "_scsd:*:31:31:Service Configuration Service:/var/empty:/usr/bin/false\n",
      "_ces:*:32:32:Certificate Enrollment Service:/var/empty:/usr/bin/false\n",
      "\n",
      "_appstore:*:33:33:Mac App Store Service:/var/db/appstore:/usr/bin/false\n",
      "_mcxalr:*:54:54:MCX AppLaunch:/var/empty:/usr/bin/false\n",
      "_appleevents:*:55:55:AppleEvents Daemon:/var/empty:/usr/bin/false\n",
      "_geod:*:56:56:Geo Services Daemon:/var/db/geod:/usr/bin/false\n",
      "_devdocs:*:59:59:Developer Documentation:/var/empty:/usr/bin/false\n",
      "_sandbox:*:60:60:Seatbelt:/var/empty:/usr/bin/false\n",
      "_mdnsresponder:*:65:65:mDNSResponder:/var/empty:/usr/bin/false\n",
      "\n",
      "_ard:*:67:67:Apple Remote Desktop:/var/empty:/usr/bin/false\n",
      "_www:*:70:70:World Wide Web Server:/Library/WebServer:/usr/bin/false\n",
      "_eppc:*:71:71:Apple Events User:/var/empty:/usr/bin/false\n",
      "_cvs:*:72:72:CVS Server:/var/empty:/usr/bin/false\n",
      "_svn:*:73:73:SVN Server:/var/empty:/usr/bin/false\n",
      "_mysql:*:74:74:MySQL Server:/var/empty:/usr/bin/false\n",
      "_sshd:*:75:75:sshd Privilege separation:/var/empty:/usr/bin/false\n",
      "\n",
      "_qtss:*:76:76:QuickTime Streaming Server:/var/empty:/usr/bin/false\n",
      "_cyrus:*:77:6:Cyrus Administrator:/var/imap:/usr/bin/false\n",
      "_mailman:*:78:78:Mailman List Server:/var/empty:/usr/bin/false\n",
      "_appserver:*:79:79:Application Server:/var/empty:/usr/bin/false\n",
      "_clamav:*:82:82:ClamAV Daemon:/var/virusmails:/usr/bin/false\n",
      "_amavisd:*:83:83:AMaViS Daemon:/var/virusmails:/usr/bin/false\n",
      "_jabber:*:84:84:Jabber XMPP Server:/var/empty:/usr/bin/false\n",
      "\n",
      "_appowner:*:87:87:Application Owner:/var/empty:/usr/bin/false\n",
      "_windowserver:*:88:88:WindowServer:/var/empty:/usr/bin/false\n",
      "_spotlight:*:89:89:Spotlight:/var/empty:/usr/bin/false\n",
      "_tokend:*:91:91:Token Daemon:/var/empty:/usr/bin/false\n",
      "_securityagent:*:92:92:SecurityAgent:/var/db/securityagent:/usr/bin/false\n",
      "_calendar:*:93:93:Calendar:/var/empty:/usr/bin/false\n",
      "_teamsserver:*:94:94:TeamsServer:/var/teamsserver:/usr/bin/false\n",
      "\n",
      "_update_sharing:*:95:-2:Update Sharing:/var/empty:/usr/bin/false\n",
      "_installer:*:96:-2:Installer:/var/empty:/usr/bin/false\n",
      "_atsserver:*:97:97:ATS Server:/var/empty:/usr/bin/false\n",
      "_ftp:*:98:-2:FTP Daemon:/var/empty:/usr/bin/false\n",
      "_unknown:*:99:99:Unknown User:/var/empty:/usr/bin/false\n",
      "_softwareupdate:*:200:200:Software Update Service:/var/db/softwareupdate:/usr/bin/false\n",
      "_coreaudiod:*:202:202:Core Audio Daemon:/var/empty:/usr/bin/false\n",
      "\n",
      "_screensaver:*:203:203:Screensaver:/var/empty:/usr/bin/false\n",
      "_locationd:*:205:205:Location Daemon:/var/db/locationd:/usr/bin/false\n",
      "_trustevaluationagent:*:208:208:Trust Evaluation Agent:/var/empty:/usr/bin/false\n",
      "_timezone:*:210:210:AutoTimeZoneDaemon:/var/empty:/usr/bin/false\n",
      "_lda:*:211:211:Local Delivery Agent:/var/empty:/usr/bin/false\n",
      "_cvmsroot:*:212:212:CVMS Root:/var/empty:/usr/bin/false\n",
      "_usbmuxd:*:213:213:iPhone OS Device Helper:/var/db/lockdown:/usr/bin/false\n",
      "\n",
      "_dovecot:*:214:6:Dovecot Administrator:/var/empty:/usr/bin/false\n",
      "_dpaudio:*:215:215:DP Audio:/var/empty:/usr/bin/false\n",
      "_postgres:*:216:216:PostgreSQL Server:/var/empty:/usr/bin/false\n",
      "_krbtgt:*:217:-2:Kerberos Ticket Granting Ticket:/var/empty:/usr/bin/false\n",
      "_kadmin_admin:*:218:-2:Kerberos Admin Service:/var/empty:/usr/bin/false\n",
      "_kadmin_changepw:*:219:-2:Kerberos Change Password Service:/var/empty:/usr/bin/false\n",
      "_devicemgr:*:220:220:Device Management Server:/var/empty:/usr/bin/false\n",
      "\n",
      "_webauthserver:*:221:221:Web Auth Server:/var/empty:/usr/bin/false\n",
      "_netbios:*:222:222:NetBIOS:/var/empty:/usr/bin/false\n",
      "_warmd:*:224:224:Warm Daemon:/var/empty:/usr/bin/false\n",
      "_dovenull:*:227:227:Dovecot Authentication:/var/empty:/usr/bin/false\n",
      "_netstatistics:*:228:228:Network Statistics Daemon:/var/empty:/usr/bin/false\n",
      "_avbdeviced:*:229:-2:Ethernet AVB Device Daemon:/var/empty:/usr/bin/false\n",
      "_krb_krbtgt:*:230:-2:Open Directory Kerberos Ticket Granting Ticket:/var/empty:/usr/bin/false\n",
      "\n",
      "_krb_kadmin:*:231:-2:Open Directory Kerberos Admin Service:/var/empty:/usr/bin/false\n",
      "_krb_changepw:*:232:-2:Open Directory Kerberos Change Password Service:/var/empty:/usr/bin/false\n",
      "_krb_kerberos:*:233:-2:Open Directory Kerberos:/var/empty:/usr/bin/false\n",
      "_krb_anonymous:*:234:-2:Open Directory Kerberos Anonymous:/var/empty:/usr/bin/false\n",
      "_assetcache:*:235:235:Asset Cache Service:/var/empty:/usr/bin/false\n",
      "_coremediaiod:*:236:236:Core Media IO Daemon:/var/empty:/usr/bin/false\n",
      "_launchservicesd:*:239:239:_launchservicesd:/var/empty:/usr/bin/false\n",
      "\n",
      "_iconservices:*:240:240:IconServices:/var/empty:/usr/bin/false\n",
      "_distnote:*:241:241:DistNote:/var/empty:/usr/bin/false\n",
      "_nsurlsessiond:*:242:242:NSURLSession Daemon:/var/db/nsurlsessiond:/usr/bin/false\n",
      "_displaypolicyd:*:244:244:Display Policy Daemon:/var/empty:/usr/bin/false\n",
      "_astris:*:245:245:Astris Services:/var/db/astris:/usr/bin/false\n",
      "_krbfast:*:246:-2:Kerberos FAST Account:/var/empty:/usr/bin/false\n",
      "_gamecontrollerd:*:247:247:Game Controller Daemon:/var/empty:/usr/bin/false\n",
      "\n",
      "_mbsetupuser:*:248:248:Setup User:/var/setup:/bin/bash\n",
      "_ondemand:*:249:249:On Demand Resource Daemon:/var/db/ondemand:/usr/bin/false\n",
      "_xserverdocs:*:251:251:macOS Server Documents Service:/var/empty:/usr/bin/false\n",
      "_wwwproxy:*:252:252:WWW Proxy:/var/empty:/usr/bin/false\n",
      "_mobileasset:*:253:253:MobileAsset User:/var/ma:/usr/bin/false\n",
      "_findmydevice:*:254:254:Find My Device Daemon:/var/db/findmydevice:/usr/bin/false\n",
      "_datadetectors:*:257:257:DataDetectors:/var/db/datadetectors:/usr/bin/false\n",
      "\n",
      "_captiveagent:*:258:258:captiveagent:/var/empty:/usr/bin/false\n",
      "_ctkd:*:259:259:ctkd Account:/var/empty:/usr/bin/false\n",
      "_applepay:*:260:260:applepay Account:/var/db/applepay:/usr/bin/false\n",
      "_hidd:*:261:261:HID Service User:/var/db/hidd:/usr/bin/false\n",
      "_cmiodalassistants:*:262:262:CoreMedia IO Assistants User:/var/db/cmiodalassistants:/usr/bin/false\n",
      "_analyticsd:*:263:263:Analytics Daemon:/var/db/analyticsd:/usr/bin/false\n",
      "_fpsd:*:265:265:FPS Daemon:/var/db/fpsd:/usr/bin/false\n",
      "\n",
      "_timed:*:266:266:Time Sync Daemon:/var/db/timed:/usr/bin/false\n",
      "_nearbyd:*:268:268:Proximity and Ranging Daemon:/var/db/nearbyd:/usr/bin/false\n",
      "_reportmemoryexception:*:269:269:ReportMemoryException:/var/db/reportmemoryexception:/usr/bin/false\n",
      "_driverkit:*:270:270:DriverKit:/var/empty:/usr/bin/false\n",
      "_diskimagesiod:*:271:271:DiskImages IO Daemon:/var/db/diskimagesiod:/usr/bin/false\n",
      "_logd:*:272:272:Log Daemon:/var/db/diagnostics:/usr/bin/false\n",
      "_appinstalld:*:273:273:App Install Daemon:/var/db/appinstalld:/usr/bin/false\n",
      "\n",
      "_installcoordinationd:*:274:274:Install Coordination Daemon:/var/db/installcoordinationd:/usr/bin/false\n",
      "_demod:*:275:275:Demo Daemon:/var/empty:/usr/bin/false\n",
      "_rmd:*:277:277:Remote Management Daemon:/var/db/rmd:/usr/bin/false\n",
      "_fud:*:278:278:Firmware Update Daemon:/var/db/fud:/usr/bin/false\n",
      "_knowledgegraphd:*:279:279:Knowledge Graph Daemon:/var/db/knowledgegraphd:/usr/bin/false\n",
      "_coreml:*:280:280:CoreML Services:/var/empty:/usr/bin/false\n",
      "_trustd:*:282:282:trustd:/var/empty:/usr/bin/false\n",
      "\n",
      "_oahd:*:441:441:OAH Daemon:/var/empty:/usr/bin/false\n",
      "\n"
     ]
    }
   ],
   "source": [
    "def read_n(filename, n):\n",
    "    with open(filename) as f:\n",
    "        \n",
    "        while True:\n",
    "            output = ''.join(f.readline()  # generator expression\n",
    "                             for i in range(n))\n",
    "\n",
    "            if output:  # if it's not an empty string\n",
    "                yield output\n",
    "            else:\n",
    "                break\n",
    "        \n",
    "for one_chunk in read_n('/etc/passwd', 7):\n",
    "    print(one_chunk)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Exercise: `once_per_minute`\n",
    "\n",
    "Normally, we want to be able to run a function on our own schedule, whenever it's good for us. *BUT* some functions are real resource hogs, and we don't want to run them too often.  \n",
    "\n",
    "Exercise: Write a decorator that ensures a function can only be run once in any 60-second period."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "5\n",
      "11\n"
     ]
    },
    {
     "ename": "RunTooOftenError",
     "evalue": "Wait longer before running add",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mRunTooOftenError\u001b[0m                          Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-19-a9e38e2db51e>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m     27\u001b[0m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0madd\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;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     28\u001b[0m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mmul\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;36m5\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;36m6\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 29\u001b[0;31m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0madd\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;36m10\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;36m4\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m     30\u001b[0m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mmul\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;36m8\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;36m15\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m<ipython-input-19-a9e38e2db51e>\u001b[0m in \u001b[0;36mwrapper\u001b[0;34m(*args)\u001b[0m\n\u001b[1;32m     11\u001b[0m         \u001b[0mcurrent_time\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mtime\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mtime\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     12\u001b[0m         \u001b[0;32mif\u001b[0m \u001b[0mcurrent_time\u001b[0m \u001b[0;34m-\u001b[0m \u001b[0mlast_ran_at\u001b[0m \u001b[0;34m<\u001b[0m \u001b[0;36m60\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 13\u001b[0;31m             \u001b[0;32mraise\u001b[0m \u001b[0mRunTooOftenError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34mf'Wait longer before running {func.__name__}'\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m     14\u001b[0m         \u001b[0mlast_ran_at\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mcurrent_time\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     15\u001b[0m         \u001b[0mvalue\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mfunc\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m*\u001b[0m\u001b[0margs\u001b[0m\u001b[0;34m)\u001b[0m  \u001b[0;31m# LEGB rule -- local, enclosing, global, builtin\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mRunTooOftenError\u001b[0m: Wait longer before running add"
     ]
    }
   ],
   "source": [
    "import time\n",
    "\n",
    "class RunTooOftenError(Exception):\n",
    "    pass\n",
    "\n",
    "def once_per_minute(func):  # decorator functions take the func as arg\n",
    "    last_ran_at = 0\n",
    "    def wrapper(*args):\n",
    "        nonlocal last_ran_at\n",
    "\n",
    "        current_time = time.time()\n",
    "        if current_time - last_ran_at < 60:\n",
    "            raise RunTooOftenError(f'Wait longer before running {func.__name__}')\n",
    "        last_ran_at = current_time\n",
    "        value = func(*args)  # LEGB rule -- local, enclosing, global, builtin\n",
    "        return value\n",
    "    return wrapper    \n",
    "\n",
    "@once_per_minute     # same as: add = once_per_minute(add)\n",
    "def add(a, b):\n",
    "    return a + b\n",
    "\n",
    "@once_per_minute\n",
    "def mul(a, b):\n",
    "    return a + b\n",
    "\n",
    "print(add(2, 3))\n",
    "print(mul(5, 6))\n",
    "print(add(10, 4))\n",
    "print(mul(8, 15))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "5\n",
      "11\n",
      "14\n",
      "23\n"
     ]
    }
   ],
   "source": [
    "import time\n",
    "\n",
    "class RunTooOftenError(Exception):\n",
    "    pass\n",
    "\n",
    "# If I want my decorator to take an argument,\n",
    "# I have to use THREE functions!\n",
    "# Outer one -- gets the argument\n",
    "# Middle one -- gets the funcion\n",
    "# Inner one -- called each time we invoke the original function name\n",
    "\n",
    "def once_per_n(n): \n",
    "    def middle(func):\n",
    "\n",
    "        last_ran_at = 0\n",
    "        def wrapper(*args):\n",
    "            nonlocal last_ran_at\n",
    "\n",
    "            current_time = time.time()\n",
    "            if current_time - last_ran_at < n:\n",
    "                raise RunTooOftenError(f'Wait longer before running {func.__name__}')\n",
    "            last_ran_at = current_time\n",
    "            value = func(*args)  # LEGB rule -- local, enclosing, global, builtin\n",
    "            return value\n",
    "        return wrapper    \n",
    "    return middle\n",
    "\n",
    "@once_per_n(0)\n",
    "def add(a, b):\n",
    "    return a + b\n",
    "\n",
    "@once_per_n(0)\n",
    "def mul(a, b):\n",
    "    return a + b\n",
    "\n",
    "print(add(2, 3))\n",
    "print(mul(5, 6))\n",
    "print(add(10, 4))\n",
    "print(mul(8, 15))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Now running once_per_n(0)\n",
      "Now running loud_deco\n",
      "Now running once_per_n(0)\n",
      "Now running loud_deco\n",
      "Now running loud_deco/wrapper\n",
      "Now running once_per_n/wrapper\n",
      "5\n",
      "Now running loud_deco/wrapper\n",
      "Now running once_per_n/wrapper\n",
      "11\n",
      "Now running loud_deco/wrapper\n",
      "Now running once_per_n/wrapper\n",
      "14\n",
      "Now running loud_deco/wrapper\n",
      "Now running once_per_n/wrapper\n",
      "23\n"
     ]
    }
   ],
   "source": [
    "def once_per_n(n): \n",
    "    print(f'Now running once_per_n({n})')\n",
    "    def middle(func):\n",
    "\n",
    "        last_ran_at = 0\n",
    "        def wrapper(*args):\n",
    "            print(f'Now running once_per_n/wrapper')\n",
    "            nonlocal last_ran_at\n",
    "\n",
    "            current_time = time.time()\n",
    "            if current_time - last_ran_at < n:\n",
    "                raise RunTooOftenError(f'Wait longer before running {func.__name__}')\n",
    "            last_ran_at = current_time\n",
    "            value = func(*args)  # LEGB rule -- local, enclosing, global, builtin\n",
    "            return value\n",
    "        return wrapper    \n",
    "    return middle\n",
    "\n",
    "def loud_deco(func):\n",
    "    print(f'Now running loud_deco')\n",
    "    def wrapper(*args):\n",
    "        print(f'Now running loud_deco/wrapper')\n",
    "        value = func(*args)\n",
    "        return value\n",
    "    return wrapper\n",
    "\n",
    "@loud_deco\n",
    "@once_per_n(0)\n",
    "def add(a, b):\n",
    "    return a + b\n",
    "\n",
    "@loud_deco\n",
    "@once_per_n(0)\n",
    "def mul(a, b):\n",
    "    return a + b\n",
    "\n",
    "print(add(2, 3))\n",
    "print(mul(5, 6))\n",
    "print(add(10, 4))\n",
    "print(mul(8, 15))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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