</p> <p>This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. </p> <p>If you did not receive a copy of the PHP license, or have any questions about PHP licensing, please contact license@php.net. </p> </td></tr> </table> </div></body></html>这一段是html语言吗？为什么请求网页后编写title = etree.xpath('/html/body/div[1]/div[1]/div[2]/ul/li/a/text()')会是一个空列表（在 xpath helper下可以输出结果）

不完全是HTML语言，它包含HTML标签和一些文本内容。这段代码是PHP的许可证声明。

至于你的第二个问题，可能是因为你的XPath表达式没有匹配到任何内容。你可以尝试使用Chrome浏览器的开发者工具，在Elements标签下查看网页的DOM结构，确认XPath表达式的正确性。另外，也可以尝试使用相对路径或更简洁的XPath表达式来匹配元素。

相关问题

<?xml version="1.0" encoding="UTF-8"?> <?xml-stylesheet type="text/xsl" href="configuration.xsl"?> <!-- Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. See accompanying LICENSE file. --> <!-- Put site-specific property overrides in this file. --> <configuration> <property> <name>fs.defaultFS</name> <value>hdfs://localhost:9000</value> </property> <property> <name>hadoop.tmp.dir</name> <value>D:\Development\Hadoop\data\tmp</value> </property> </configuration> 检查一下规范性

这个XML文档中的XML声明是符合规范的，指定了XML版本为1.0，编码方式为UTF-8。其次，这个XML文档中包含了一个XML样式表声明，指定了用于显示该XML文档的样式表文件的路径。在注释中，这个XML文档还声明了使用Apache许可证2.0版本，以及提供了许可证的获取地址。在XML元素中，使用了<configuration>元素作为根元素，并包含了两个<property>元素，用来定义Hadoop的配置属性。整个XML文档结构合乎XML规范，没有语法错误。

/** * Returns <code>true</code> as soon as the lock is acquired. * If the lock is currently held by another thread in this or any * other process in the distributed system this method keeps trying * to acquire the lock for up to <code>waitTime</code> before * giving up and returning <code>false</code>. If the lock is acquired, * it is held until <code>unlock</code> is invoked, or until <code>leaseTime</code> * have passed since the lock was granted - whichever comes first. * * @param waitTime the maximum time to aquire the lock * @param leaseTime lease time * @param unit time unit * @return <code>true</code> if lock has been successfully acquired * @throws InterruptedException - if the thread is interrupted before or during this method. */

这段代码看起来是一个方法的注释，它描述了一个分布式系统中的锁的获取方法。该方法会在尝试一定时间后，如果没有获取到锁，就返回 false；如果获取到了锁，锁会一直保持到 unlock 方法被调用，或者到指定的时间 leaseTime 到期。在这个过程中，如果线程被中断，该方法会抛出 InterruptedException 异常。