Examples of creating and using decorators in Python

decorators.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Decorator Examples"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "('HELLO', 'UPPER', 'WORLD')\n"
     ]
    }
   ],
   "source": [
    "def upper(fn):\n",
    "    def wrapper(*args):\n",
    "        args = [str(a).upper() for a in args]\n",
    "        return fn(*args)\n",
    "    return wrapper\n",
    "    \n",
    "@upper\n",
    "def just_print(*strings):\n",
    "    print(strings)\n",
    "      \n",
    "just_print(\"hello\", \"upper\", \"world\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1035.0\n",
      "5175.0\n",
      "0\n"
     ]
    }
   ],
   "source": [
    "def apply_interest_rate(rate):\n",
    "    def decorator(fn):\n",
    "        def wrapper(*args):\n",
    "            args = [\n",
    "                a * (1+rate) \n",
    "                if a <= 10000 else 0\n",
    "                for a in args\n",
    "            ]\n",
    "            return fn(*args)\n",
    "        return wrapper\n",
    "    return decorator\n",
    "    \n",
    "@apply_interest_rate(0.035)\n",
    "def create_loans(*amounts):\n",
    "    for amount in amounts:\n",
    "        print(amount)\n",
    "\n",
    "create_loans(1000, 5000, 20000)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "some\n",
      "very\n",
      "very\n",
      "special\n",
      "logging\n",
      "do_work\n",
      "doing some more work\n"
     ]
    }
   ],
   "source": [
    "def special_logger(fn):\n",
    "    # anything done here will happen \n",
    "    # when decorator is set, not called\n",
    "    def w():\n",
    "        print(\"some\")\n",
    "        print(\"very\")\n",
    "        print(\"very\")\n",
    "        print(\"special\")\n",
    "        print(\"logging\")\n",
    "        print(fn.__name__)\n",
    "        return fn()\n",
    "    return w\n",
    "\n",
    "@special_logger\n",
    "def do_work():\n",
    "    print(\"doing some more work\")\n",
    "    \n",
    "do_work()    "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "adding some awesome while...\n",
      "doing some stuff\n",
      "---------\n",
      "no more boring, just awesomeness!\n",
      "---------\n",
      "Hello Ruby\n",
      "---------\n"
     ]
    }
   ],
   "source": [
    "import time\n",
    "\n",
    "class awesome:\n",
    "    def add(fn):\n",
    "        def wrap():\n",
    "            print(\"adding some awesome while...\")\n",
    "            return fn()\n",
    "        return wrap\n",
    "    \n",
    "    def swap(fn):\n",
    "        def replacement():\n",
    "            print(\"no more boring, just awesomeness!\")\n",
    "        return replacement\n",
    "    \n",
    "    def pause(seconds):\n",
    "        def decor(fn):\n",
    "            def wrap(name):\n",
    "                time.sleep(seconds)\n",
    "                return fn(name)\n",
    "            return wrap\n",
    "        return decor\n",
    "    \n",
    "\n",
    "\n",
    "@awesome.add\n",
    "def some_stuff():\n",
    "    print(\"doing some stuff\")\n",
    "\n",
    "@awesome.swap\n",
    "def boring():\n",
    "    print(\"so boring\")\n",
    "        \n",
    "@awesome.pause(5)\n",
    "def hello(name):\n",
    "    print(f\"Hello {name}\")\n",
    "    \n",
    "some_stuff()\n",
    "print(\"---------\")\n",
    "boring()\n",
    "print(\"---------\")\n",
    "hello(\"Ruby\")\n",
    "print(\"---------\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Execution time: 5.000079154968262\n"
     ]
    }
   ],
   "source": [
    "from time import time, sleep\n",
    "\n",
    "def timely(fn):\n",
    "    def wrapper(*args, **kwargs):\n",
    "        start = time()\n",
    "        result = fn(*args, **kwargs)\n",
    "        end = time()\n",
    "        print(\"Execution time: {}\".format(end - start))\n",
    "        return result\n",
    "    return wrapper\n",
    "\n",
    "@timely\n",
    "def sleepy():\n",
    "    # function will take\n",
    "    # at least 5 seconds\n",
    "    sleep(5)\n",
    "    \n",
    "sleepy()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Whee!\n",
      "Whee!\n",
      "---------\n",
      "Hello Jody\n",
      "Hello Jody\n",
      "Hello Jody\n",
      "Hello Jody\n",
      "Hello Jody\n"
     ]
    }
   ],
   "source": [
    "def repeat(fn=None, times=2):\n",
    "    def decorator(func):\n",
    "        def wrapper(*args, **kwargs):\n",
    "            for _ in range(times):\n",
    "                value = func(*args, **kwargs)\n",
    "            return value\n",
    "        return wrapper\n",
    "\n",
    "    if fn is None:\n",
    "        return decorator\n",
    "    else:\n",
    "        return decorator(fn)\n",
    "    \n",
    "@repeat\n",
    "def say_whee():\n",
    "    print(\"Whee!\")\n",
    "\n",
    "@repeat(times=5)\n",
    "def howdy(name):\n",
    "    print(f\"Hello {name}\")\n",
    "    \n",
    "\n",
    "say_whee()    \n",
    "print(\"---------\")\n",
    "howdy(\"Jody\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 69,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "<div>HELLO-UPPER-WORLD</div>\n"
     ]
    }
   ],
   "source": [
    "# HTML Wrapper with Decorators\n",
    "\n",
    "def bookend(tag):\n",
    "    left = f\"<{tag}>\"\n",
    "    right = f\"</{tag}>\"\n",
    "    def decor_bookend(fn):\n",
    "        def wrapper(string):\n",
    "            return fn(left + string + right)\n",
    "        return wrapper\n",
    "    return decor_bookend\n",
    "    \n",
    "\n",
    "def hyphens(fn):\n",
    "    def wrapper(*args):\n",
    "        return fn(\"-\".join([str(a) for a in args]))\n",
    "    return wrapper\n",
    "    \n",
    "\n",
    "def upper(fn):\n",
    "    def wrapper(*args):\n",
    "        args = [str(a).upper() for a in args]\n",
    "        return fn(*args)\n",
    "    return wrapper\n",
    "\n",
    "@upper\n",
    "@hyphens\n",
    "@bookend(\"div\")\n",
    "def just_print(*strings):\n",
    "    print(*strings)\n",
    "      \n",
    "just_print(\"hello\", \"upper\", \"world\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'<div>HELLO-UPPER-WORLD</div>'"
      ]
     },
     "execution_count": 22,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# HTML Wrapper without Decorators\n",
    "  \n",
    "def bookend_not_decorator(tag):\n",
    "    left = f\"<{tag}>\"\n",
    "    right = f\"</{tag}>\"\n",
    "    def tagged(string):\n",
    "        return left + string + right\n",
    "    return tagged\n",
    "\n",
    "def hyphens(*args):\n",
    "    return \"-\".join([str(a) for a in args])\n",
    "    \n",
    "\n",
    "def upper(*args):\n",
    "    return [str(a).upper() for a in args]\n",
    "\n",
    "\n",
    "# bookend(\"div\")(print)(\n",
    "#     hyphens(\n",
    "#         *upper(\"hello\", \"upper\", \"world\")\n",
    "#     )\n",
    "# )\n",
    "\n",
    "bookend_not_decorator(\"div\")(\n",
    "    hyphens(\n",
    "        *upper(\"hello\", \"upper\", \"world\")\n",
    "    )\n",
    ")"
   ]
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "Python 3",
   "language": "python",
   "name": "python3"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 3
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.7.4"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 2
}

Notice that in the last example, we are NOT using decorators and yet achieve the same result.

In fact, we are using a couple of simple functions and a closure.

Like many features in Python, decorators may not always provide the simplest (or even Pythonic) way to write code.

Use wisely.