正则表达式-贪婪与懒惰
事故：
今天写vpnbook.py的时候（参见vpnbook.py），遇到一个问题，匹配到太多的数据，而且是我不需要的。
我要对某个html进行解析，又为了跨平台和快速使用，就没有使用第三方库（比如BeautifulSoup）
获得的html如下
1 <!DOCTYPE html> 2 3 <!--[if lt IE 7 ]><html class="ie ie6 no-js" lang="en"> <![endif]--> 4 5 <!--[if IE 7 ]><html class="ie ie7 no-js" lang="en"> <![endif]--> 6 7 <!--[if IE 8 ]><html class="ie ie8 no-js" lang="en"> <![endif]--> 8 9 <!--[if IE 9 ]><html class="ie ie9 no-js" lang="en"> <![endif]--> 10 11 <!--[if (gte IE 9)|!(IE)]><!--><html class="no-js" lang="en"> <!--<![endif]--> 12 13 <head> 14 15 <meta charset="utf-8"> 16 17 <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> 18 19 20 21 <title>Free VPN Accounts • 100% Free PPTP and OpenVPN Service</title> 22 23 <meta name="description" content="Free VPN Service – VPNBook.com is the #1 premium Free VPN Server account provider. US, UK, and offshore VPN servers available."> 24 25 <meta name="keywords" content="free vpn, free vpn service, free vpn server, free vpn account, openvpn, pptp vpn, web proxy" /> 26 27 <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=0"> 28 29 <meta name="apple-mobile-web-app-capable" content="yes"> 30 31 32 33 <link rel="stylesheet" href="/css/skeleton-v1.1.css"> 34 35 <link rel="stylesheet" href="/css/flexslider-v1.8.css"> 36 37 <link rel="stylesheet" href="/css/main-r6.css?0211"> 38 39 <link rel="stylesheet" href="/css/media-queries-r6.css"> 40 41 <link rel="stylesheet" href="/css/sprites-r6.css"> 42 43 <link rel="stylesheet" href="/css/theme-default-r6.css"> 44 45 <link href='https://fonts.googleapis.com/css?family=Open+Sans:400,600,400italic' rel='stylesheet' type='text/css'> 46 47 48 49 <link rel="shortcut icon" href="/images/favicon.ico"> 50 51 <link rel="apple-touch-icon" href="/images/apple-touch-icon.png"> 52 53 <link rel="apple-touch-icon" sizes="72x72" href="/images/apple-touch-icon-72x72.png"> 54 55 <link rel="apple-touch-icon" sizes="114x114" href="/images/apple-touch-icon-114x114.png"> 56 57 58 59 <!-- Allow IE to render HTML5 --> 60 61 <!--[if lt IE 9]> 62 63 <script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script> 64 65 <![endif]--> 66 67 68 69 <script> 70 71 (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){ 72 73 (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o), 74 75 m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m) 76 77 })(window,document,'script','//www.google-analytics.com/analytics.js','ga'); 78 79 ga('create', 'UA-40096058-1', 'vpnbook.com'); 80 81 ga('send', 'pageview'); 82 83 </script> 84 85 86 87 </head> 88 89 90 91 <body> 92 93 <div id="main" role="main"> 94 95 96 97 <header> 98 99 <div class="container"> 100 101 <h1 class="logo one-third column alpha"> 102 103 <a href="/"> 104 105 <img src="/images/logo.png" alt="Free VPN" class="scale-with-grid" /> 106 107 <img src="/images/logo-mobile.png" class="scale-with-grid mobile-only" alt="" /><!-- Alternative image for mobile devices --> 108 109 </a> 110 111 </h1> 112 113 114 115 <nav class="menu two-thirds column omega"> 116 117 <ul> 118 119 <li><a href="/" >VPNBook<br /><span>news</span></a></li> 120 121 <li><a href="/freevpn" class='active'>Free VPN<br /><span>accounts</span></a></li> 122 123 <li><a href="/webproxy" >Free Web<br /><span>proxy</span></a></li> 124 125 <li><a href="/howto" >How-To<br /><span>setup</span></a></li> 126 127 <li><a href="/features" >Features<br /><span>service</span></a></li> 128 129 <li><a href="/contact" >Privacy<br /><span>contact</span></a></li> 130 131 </ul> 132 133 </nav> 134 135 </div><!-- .container --> 136 137 138 139 <div class="bottom-gradient"> 140 141 <span class="left"></span> 142 143 <span class="center"></span> 144 145 <span class="right"></span> 146 147 </div> 148 149 </header> 150 151 152 153 <article id="pricing"> 154 155 <div class="container"> 156 157 158 159 <div class="sixteen columns titleset"> 160 161 <h2 class="remove-bottom">Free VPN</h2> 162 163 <h6 class="subheader">PPTP and OpenVPN Accounts<br> </h6> 164 165 166 167 <div class="align-center adsense"> 168 <script type="text/javascript"><!-- 169 google_ad_client = /* Vpnbook LB-1 */ 170 "ca-pub-3860002410887566"; 171 google_ad_slot = "5227255820"; 172 google_ad_width = 728; 173 google_ad_height = 90; 174 //--> 175 </script> 176 <script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script> 177 </div> 178 </div> 179 180 181 182 <div class="one-third column"> 183 184 <div class="headset price clearfix"> 185 186 <img src="/images/empty.gif" alt="" class="large-icons icon-font" /> 187 188 <h4>Free PPTP VPN</h4> 189 190 <span><sup>$</sup>0<sub>/mo</sub></span> 191 192 </div> 193 194 <div class="bottom-gradient add-top add-bottom"> 195 196 <span class="left"></span> 197 198 <span class="center"></span> 199 200 <span class="right"></span> 201 202 </div> 203 204 <p>PPTP (point to point tunneling) is widely used since it is supported across all Microsoft Windows, 205 206 Linux, Apple, Mobile and PS3 platforms. It is however easier to block and might not work if your ISP or 207 208 government blocks the protocol. In that case you need to use OpenVPN, which is impossible to detect or block.</p> 209 210 211 212 <ul class="disc"> 213 214 <li><strong>euro195.vpnbook.com</strong></li> 215 216 <li><strong>euro213.vpnbook.com</strong></li> 217 218 <li><strong>uk180.vpnbook.com</strong> <span class="red">(UK VPN - optimized for fast web surfing; no p2p downloading)</span></li> 219 220 <li><strong>us1.vpnbook.com</strong> <span class="red">(US VPN - optimized for fast web surfing; no p2p downloading)</span></li> 221 222 <li>Username: <strong>vpnbook</strong></li> 223 224 <li>Password: <strong>bRudre3u</strong></li> 225 226 </ul> 227 228 229 230 <div><strong><span class="green"> More servers coming. Please Donate.</span></strong></div> 231 232 233 234 </div><!-- .columns --> 235 236 237 238 239 240 <div class="one-third column box light featured"> 241 242 <div class="headset price clearfix"> 243 244 <img src="/images/empty.gif" alt="" class="large-icons icon-font" /> 245 246 <h4>Free OpenVPN <br><small>(Recommended)</small></h4> 247 248 <span><sup>$</sup>0<sub>/mo</sub></span> 249 250 </div> 251 252 253 254 <div class="bottom-gradient add-top add-bottom"> 255 256 <span class="left"></span> 257 258 <span class="center"></span> 259 260 <span class="right"></span> 261 262 </div> 263 264 265 266 <p>OpenVPN is the best and most recommended open-source VPN software world-wide. It is the most secure VPN option. 267 268 You need to download the open-source <a href="/howto">OpenVPN Client</a> and our configuration and certificate bundle 269 270 from the links below (use TCP if you cannot connect to UDP due to network restriction).</p> 271 272 273 274 <ul class="disc"> 275 276 <li><a href="/free-openvpn-account/VPNBook.com-OpenVPN-Euro1.zip">Euro1 OpenVPN Certificate Bundle</a> </li> 277 278 <li><a href="/free-openvpn-account/VPNBook.com-OpenVPN-Euro2.zip">Euro2 OpenVPN Certificate Bundle</a> </li> 279 280 <li><a href="/free-openvpn-account/VPNBook.com-OpenVPN-UK1.zip">UK OpenVPN Certificate Bundle</a> <span class="red">(optimized for fast web surfing; no p2p downloading)</span></li> 281 282 <li><a href="/free-openvpn-account/VPNBook.com-OpenVPN-US1.zip">US OpenVPN Certificate Bundle</a> <span class="red">(optimized for fast web surfing; no p2p downloading)</span></li> 283 284 <li>All bundles include UDP53, UDP 25000, TCP 80, TCP 443 profile</li> 285 286 <li>Username: <strong>vpnbook</strong></li> 287 288 <li>Password: <strong>bRudre3u</strong></li> 289 290 </ul> 291 292 <a class="button featured animate">Choose an OpenVPN Server from above</a> 293 294 </div><!-- .columns --> 295 296 297 298 <div class="one-third column"> 299 300 <div class="headset price clearfix"> 301 302 <img src="/images/empty.gif" alt="" class="large-icons icon-burst" /> 303 304 <h4>Donate</h4> 305 306 307 308 </div> 309 310 <div class="bottom-gradient add-top add-bottom"> 311 312 <span class="left"></span> 313 314 <span class="center"></span> 315 316 <span class="right"></span> 317 318 </div> 319 320 321 322 <div class="align-center" id="paypalDonate"> 323 324 <iframe src="http://causera.org/donation_app/r?i=4e1bf7d46c3e3c1747fc0a588042e547" id="wiframe" style="width: 205px; height: 163px; border: 0px; overflow: hidden;" scrolling="no"></iframe> 325 326 </div> 327 328 329 330 <div class="align-center"> 331 332 <br /> 333 334 <strong>Bitcoin Donation</strong> 335 336 <br /> 337 338 <small>1FFExjn6sm2oMZ2LJsTtn1t8uXW6EE7HQ7</small> 339 340 </div> 341 342 343 344 <div class="socialMediaContainer2"> 345 346 <div class="plusoneButton"><g:plusone size="tall" href="http://www.vpnbook.com"></g:plusone></div> 347 348 <div class="facebookButton"><div id="fb-root"></div><fb:like href="http://www.vpnbook.com" send="false" layout="box_count" width="65" show_faces="false" font="arial"></fb:like></div> 349 350 <div class="twitterButton"><a href="http://twitter.com/share" rel="nofollow" class="twitter-share-button" data-url="http://www.vpnbook.com" data-text="VPNBook.com Free VPN Service" data-count="vertical">Tweet</a></div> 351 352 </div> 353 354 355 356 </div><!-- .columns --> 357 358 359 360 <div style="clear:both;"> </div> 361 362 <div class="align-center adsense"> 363 <script type="text/javascript"><!-- 364 google_ad_client = /* Vpnbook LB-2 */ 365 "ca-pub-3860002410887566"; 366 google_ad_slot = "9781879828"; 367 google_ad_width = 728; 368 google_ad_height = 90; 369 //--> 370 </script> 371 <script type="text/javascript" 372 src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> 373 </script> 374 </div> 375 376 377 </div><!-- container --> 378 379 </article> 380 381 382 383 </div><!-- #main --> 384 385 386 387 <!-- share this code --> 388 389 <!-- end share this --> 390 391 <div id="share-icons"> 392 393 <div id="share-mask"></div> 394 395 <div class="addthis_toolbox addthis_default_style addthis_32x32_style"> 396 397 <a class="addthis_button_facebook"></a> 398 399 <a class="addthis_button_twitter"></a> 400 401 <a class="addthis_button_linkedin"></a> 402 403 <a class="addthis_button_google_plusone"></a> 404 405 <a class="addthis_button_compact"></a> 406 407 </div> 408 409 <script type="text/javascript" src="http://s7.addthis.com/js/250/addthis_widget.js#pubid=ra-4f92e19745ac6401"></script> 410 411 <!-- AddThis Button END --> 412 413 414 415 <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.2/jquery.min.js"></script> 416 417 <script>if(!window.jQuery) {document.write('<script src="/js/jquery-1.8.2.min.js"><\/script>');}</script> 418 419 <script src="/js/jquery.flexslider-v1.8.min.js"></script> 420 421 <script src="/js/jquery.ba-hashchange-v1.3.min.js"></script> 422 423 <script src="/js/main-r6.js?051201"></script> 424 425 <script type="text/javascript" src="http://apis.google.com/js/plusone.js"></script> 426 427 <script src="http://connect.facebook.net/en_US/all.js#appId=221296744562462&xfbml=1"></script> 428 429 <script>!function (d, s, id) { var js, fjs = d.getElementsByTagName(s)[0], p = /^http:/.test(d.location) ? 'http' : 'https'; if (!d.getElementById(id)) { js = d.createElement(s); js.id = id; js.src = p + '://platform.twitter.com/widgets.js'; fjs.parentNode.insertBefore(js, fjs); } }(document, 'script', 'twitter-wjs');</script> 430 431 </body> 432 433 </html>
我真正需要的东西很少，如下：
<ul class="disc"> <li><strong>euro195.vpnbook.com</strong></li> <li><strong>euro213.vpnbook.com</strong></li> <li><strong>uk180.vpnbook.com</strong> <span class="red">(UK VPN - optimized for fast web surfing; no p2p downloading)</span></li> <li><strong>us1.vpnbook.com</strong> <span class="red">(US VPN - optimized for fast web surfing; no p2p downloading)</span></li> <li>Username: <strong>vpnbook</strong></li> <li>Password: <strong>bRudre3u</strong></li> </ul>
刚开始的时候我匹配 <ul class="disc">.*</ul>，正则表达式如下
m = re.search('<ul\sclass=\"disc\">.*</ul>',html,re.S)
匹配到内容却是
<ul class="disc"> <li><strong>euro195.vpnbook.com</strong></li> <li><strong>euro213.vpnbook.com</strong></li> <li><strong>uk180.vpnbook.com</strong> <span class="red">(UK VPN - optimized for fast web surfing; no p2p downloading)</span></li> <li><strong>us1.vpnbook.com</strong> <span class="red">(US VPN - optimized for fast web surfing; no p2p downloading)</span></li> <li>Username: <strong>vpnbook</strong></li> <li>Password: <strong>bRudre3u</strong></li> </ul> <div><strong><span class="green"> More servers coming. Please Donate.</span></strong></div> </div><!-- .columns --> <div class="one-third column box light featured"> <div class="headset price clearfix"> <img src="/images/empty.gif" alt="" class="large-icons icon-font" /> <h4>Free OpenVPN <br><small>(Recommended)</small></h4> <span><sup>$</sup>0<sub>/mo</sub></span> </div> <div class="bottom-gradient add-top add-bottom"> <span class="left"></span> <span class="center"></span> <span class="right"></span> </div> <p>OpenVPN is the best and most recommended open-source VPN software world-wide. It is the most secure VPN option. You need to download the open-source <a href="/howto">OpenVPN Client</a> and our configuration and certificate bundle from the links below (use TCP if you cannot connect to UDP due to network restriction).</p> <ul class="disc"> <li><a href="/free-openvpn-account/VPNBook.com-OpenVPN-Euro1.zip">Euro1 OpenVPN Certificate Bundle</a> </li> <li><a href="/free-openvpn-account/VPNBook.com-OpenVPN-Euro2.zip">Euro2 OpenVPN Certificate Bundle</a> </li> <li><a href="/free-openvpn-account/VPNBook.com-OpenVPN-UK1.zip">UK OpenVPN Certificate Bundle</a> <span class="red">(optimized for fast web surfing; no p2p downloading)</span></li> <li><a href="/free-openvpn-account/VPNBook.com-OpenVPN-US1.zip">US OpenVPN Certificate Bundle</a> <span class="red">(optimized for fast web surfing; no p2p downloading)</span></li> <li>All bundles include UDP53, UDP 25000, TCP 80, TCP 443 profile</li> <li>Username: <strong>vpnbook</strong></li> <li>Password: <strong>bRudre3u</strong></li> </ul>
也就是说，它匹配了过多的内容，我需要的是以第一个</ul>结束前的内容，也就是第一个ul标签内的所有内容。
那么，正则中有这样的匹配方式么？特此我请教了我们的大神马哥，大神曰：看文档去。
我在文档中找到了 贪婪与懒惰 这种匹配模式。
修改表达式为
m = re.search('<ul\sclass=\"disc\">.*?</ul>',html,re.S)
匹配到的数据
<ul class="disc"> <li><strong>euro195.vpnbook.com</strong></li> <li><strong>euro213.vpnbook.com</strong></li> <li><strong>uk180.vpnbook.com</strong> <span class="red">(UK VPN - optimized for fast web surfing; no p2p downloading)</span></li> <li><strong>us1.vpnbook.com</strong> <span class="red">(US VPN - optimized for fast web surfing; no p2p downloading)</span></li> <li>Username: <strong>vpnbook</strong></li> <li>Password: <strong>bRudre3u</strong></li> </ul>
仅仅多了一个问号，却是天差地别啊。
下面是 贪婪与懒惰 匹配模式的相关知识。
===================================================================================================
当正则表达式中包含能接受重复的限定符时，通常的行为是（在使整个表达式能得到匹配的前提下）匹配尽可能多的字符。以这个表达式为例：a.*b，它将会匹配最长的以a开始，以b结束的字符串。如果用它来搜索aabab的话，它会匹配整个字符串aabab。这被称为贪婪匹配。
有时，我们更需要懒惰匹配，也就是匹配尽可能少的字符。前面给出的限定符都可以被转化为懒惰匹配模式，只要在它后面加上一个问号?。这样.*?就意味着匹配任意数量的重复，但是在能使整个匹配成功的前提下使用最少的重复。现在看看懒惰版的例子吧：
a.*?b匹配最短的，以a开始，以b结束的字符串。如果把它应用于aabab的话，它会匹配aab（第一到第三个字符）和ab（第四到第五个字符）。
| 代码/语法 | 说明 |
|---|---|
| *? | 重复任意次，但尽可能少重复 |
| +? | 重复1次或更多次，但尽可能少重复 |
| ?? | 重复0次或1次，但尽可能少重复 |
| {n,m}? | 重复n到m次，但尽可能少重复 |
| {n,}? | 重复n次以上，但尽可能少重复 |
