07. Greedy and Non-Greedy Quantifiers.ipynb

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 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# <center>RegEx in Python</center>\n",
    "\n",
    "<img src=\"images/memes/meme13.jpg\" height=400 width=400>"
   ]
  },
  {
   "cell_type": "markdown",
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   "source": [
    "# Greedy Behaviour\n",
    "\n",
    "Let's consider an example."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "import re"
   ]
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   "cell_type": "code",
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   "source": [
    "txt = \"\"\"<html><head><title>Title</title>\"\"\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "pattern = re.compile(\"<.*>\")"
   ]
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   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "scrolled": true
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "['<html><head><title>Title</title>']"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
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   "source": [
    "pattern.findall(txt)"
   ]
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   "cell_type": "markdown",
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   "source": [
    "In above example, one may expect to get 4 matches, i.e. `<html>`, `<head>`, `<title>` and `</title>`. Instead, we get the longest match, i.e. `<html><head><title>Title</title>`.\n",
    "\n",
    "This particular behaviour (to find longest match) is called **greedy** behaviour.\n",
    "\n",
    "> The greedy behavior of the quantifiers is applied by default in the quantifiers. A greedy quantifier will try to match as much as possible to have the biggest match result possible.\n",
    "\n",
    "# Non-Greedy behaviour\n",
    "\n",
    "The **non-greedy** (or **reluctant**) behaviour can be requested by adding an extra question mark to the quantifier.\n",
    "\n",
    "For example, `??`, `*?` or `+?`. \n",
    "\n",
    "> A quantifier marked as reluctant will behave like the exact opposite of the greedy ones. They will try to have the smallest match possible."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [],
   "source": [
    "pattern = re.compile(\"<.*?>\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "scrolled": true
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['<html>', '<head>', '<title>', '</title>']"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "pattern.findall(txt)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "![](images/memes/meme14.jpg)"
   ]
  }
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