lxml 2.2.2 文档介绍

lxmldoc-2.2.2.pdf

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"lxmldoc-2.2.2.pdf 是关于 lxml 库的文档，主要介绍了 lxml 2.2.2 版本的相关信息，包括介绍、安装、新特性、性能基准测试以及 lxml.objectify 模块等内容。" lxml 是一个用于处理 XML 和 HTML 的 Python 库，它结合了 C 语言的高效性和 Python 的易用性。在文档的 "Introduction" 部分，lxml 提供了一个简短的概述，说明了库的主要功能和用途。文档还提供了 "Documentation" 的链接，帮助用户找到更详细的使用指南。用户可以在 "Download" 部分获取 lxml 的软件包，并通过 "Mailinglist" 和 "Bugtracker" 跟踪项目的最新进展和报告问题。lxml 的 "License" 部分则列出了软件的许可协议。 "Whylxml?" 部分解释了使用 lxml 的原因。文档指出，lxml 引擎以速度和兼容性为核心，提供了一套全面的 API，使其在处理 XML 和 HTML 数据时表现优秀。它的 "Motto" 和 "Aims" 描述了设计和开发的目标，强调了性能、灵活性和易于使用的特性。 "Installing lxml" 部分详细介绍了安装步骤和依赖项。用户需要满足特定的系统要求，然后按照指示进行安装，这包括从源代码构建 lxml 的过程。对于 Windows 和 MacOS-X 用户，文档提供了特定平台的安装建议。 " What’s new in lxml 2.0?" 介绍了这个版本的重要更新。包括对 "tree and objectify" 模块的更改，如不兼容的变化、增强功能和弃用的特性。此外，还引入了新的模块，如 lxml.usedoctest 用于文档测试，lxml.html 专注于 HTML 处理，以及 lxml.cssselect 支持 CSS 选择器。 " Benchmarks and Speed" 部分讨论了 lxml 的性能。文档给出了一般性注解，并提供了如何解读性能测试结果的方法。接着，详细对比了 lxml 在解析和序列化、ElementTree API 使用、合并不同数据源、深拷贝、树遍历、XPath 查询、以及 lxml.objectify 模块中的性能表现。lxml.objectify 提供了 "ObjectPath"，允许对象化的 XML 解析，同时实现了元素缓存和进一步的优化措施，以提高处理 XML 文档的效率。 lxml 是一个强大且高效的 Python XML 和 HTML 处理工具，其丰富的功能和优秀的性能使得它成为处理这些数据格式的首选库之一。通过详细的文档和不断更新，lxml 为开发者提供了便利的开发环境和高效的工作流。

Chapter 2

Why lxml?

2.1 Motto

“the thrills without the strangeness”

To explain the motto:

“Programming with libxml2 is like the thrilling embrace of an exotic stranger. It seems to have the

potential to fulﬁll your wildest dreams, but there’s a nagging voice somewhere in your head warning you

that you’re about to get screwed in the worst way.” (a quote by Mark Pilgrim)

Mark Pilgrim was describing in particular the experience a Python programmer has when dealing with

libxml2. The default Python bindings of libxml2 are fast, thrilling, powerful, and your code might fail

in some horrible way that you really shouldn’t have to worry about when writing Python code. lxml

combines the power of libxml2 with the ease of use of Python.

2.2 Aims

The C libraries libxml2 and libxslt have huge beneﬁts:

• Standards-compliant XML support.

• Support for (broken) HTML.

• Full-featured.

• Actively maintained by XML experts.

• fast. fast! FAST!

These libraries already ship with Python bindings, but these Python bindings mimic the C-level interface.

This yields a number of problems:

• very low level and C-ish (not Pythonic).

• underdocumented and huge, you get lost in them.

• UTF-8 in API, instead of Python unicode strings.

Chapter 4

What’s new in lxml 2.0?

During the development of the lxml 1.x series, a couple of quirks were discovered in the design that made

the API less obvious and its future extensions harder than necessary. lxml 2.0 is a soft evolution of lxml

1.x towards a simpler, more consistent and more powerful API - with some major extensions. Wherever

possible, lxml 1.3 comes close to the semantics of lxml 2.0, so that migrating should be easier for code

that currently runs with 1.3.

One of the important internal changes was the switch from the Pyrex compiler to Cython, which provides

better optimisation and improved support for newer Python language features. This allows the code of

lxml to become more Python-like again, while the performance improves as Cython continues its own

development. The code simpliﬁcation, which will continue throughout the 2.x series, will hopefully make

it even easier for users to contribute.

4.1 Changes in etree and objectify

A graduation towards a more consistent API cannot go without a certain amount of incompatible changes.

The following is a list of those diﬀerences that applications need to take into account when migrating

from lxml 1.x to lxml 2.0.

4.1.1 Incompatible changes

• lxml 0.9 introduced a feature called namespace implementation. The global Namespace factory was

added to register custom element classes and have lxml.etree look them up automatically. However,

the later development of further class lookup mechanisms made it appear less and less adequate

to register this mapping at a global level, so lxml 1.1 ﬁrst removed the namespace based lookup

from the default setup and lxml 2.0 ﬁnally removes the global namespace registry completely. As

all other lookup mechanisms, the namespace lookup is now local to a parser, including the registry

itself. Applications that use a module-level parser can easily map its get_namespace() method to

a global Namespace function to mimic the old behaviour.

• Some API functions now require passing options as keyword arguments, as opposed to positional

arguments. This restriction was introduced to make the API usage independent of future extensions

such as the addition of new positional arguments. Users should not rely on the position of an

optional argument in function signatures and instead pass it explicitly named. This also improves

code readability - it is common good practice to pass options in a consistent way independent of

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lxml 2.2.2 文档介绍

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