爲了使用XPath技術，對爬蟲抓取的網頁數據進行抽取（如標題、正文等等），花了一天的時間熟悉了一下Python語言，今天嘗試在Windows下安裝libxml2模塊，將自己的一點學習實踐簡單記錄一下。
Python在安裝一個擴展的模塊時，可以通過安裝輔助工具包（Setuptools）來安裝新的Python packages，並可以實現對已經安裝的packages的管理。在http://pypi.python.org/pypi/setuptools上你可以找到對於不同平臺下的安裝包，這些工具主要包括Python Eggs和 Easy Install。在網上搜了很多，比較常用的應該是Easy Install，而且在網站http://peak.telecommunity.com/DevCenter/EasyInstall上給出了對EasyInstall的介紹：
Easy Install is a python module (easy_install) bundled with setuptools that lets you automatically download, build, install, and manage Python packages.下面我們就一步步地準備、安裝、配置。
準備
需要的軟件包，及其相應的下載地址，分別整理如下：
Python 2.6 （python官網貌似打不開，也忘記從哪裏下載的，到網上搜一下吧）
libxml2-python-2.7.7.win32-py2.7.exe （http://xmlsoft.org/sources/win32/python/libxml2-python-2.7.7.win32-py2.7.exe，http://xmlsoft.org/sources/win32/python/）
setuptools-0.6c11.win32-py2.6.exe （http://pypi.python.org/packages/2.6/s/setuptools/setuptools-0.6c11.win32-py2.6.exe#md5=1509752c3c2e64b5d0f9589aafe053dc，http://pypi.python.org/pypi/setuptools#downloads）
安裝
第1步：安裝Python
在Windows下面，只需要安裝包的exe可行性文件即可安裝，不在累述。
第2步：安裝Easy Install工具
前提是Python要安裝好，然後安裝上面準備好的setuptools-0.6c11.win32-py2.6.exe即可，它會自動找到Python的安裝目錄，並將安裝工具包安裝到對應的目錄下面。例如我的腳本目錄爲E:\Program Files\Python26\Scripts，驗證一下：
E:\>cd E:\Program Files\Python26\Scripts
E:\Program Files\Python26\Scripts>easy_install --help
Global options:
--verbose (-v) run verbosely (default)
--quiet (-q) run quietly (turns verbosity off)
--dry-run (-n) don't actually do anything
--help (-h) show detailed help message
Options for 'easy_install' command:
--prefix installation prefix
--zip-ok (-z) install package as a zipfile
--multi-version (-m) make apps have to require() a version
--upgrade (-U) force upgrade (searches PyPI for latest
versions)
--install-dir (-d) install package to DIR
--script-dir (-s) install scripts to DIR
--exclude-scripts (-x) Don't install scripts
--always-copy (-a) Copy all needed packages to install dir
--index-url (-i) base URL of Python Package Index
--find-links (-f) additional URL(s) to search for packages
--delete-conflicting (-D) no longer needed; don't use this
--ignore-conflicts-at-my-risk no longer needed; don't use this
--build-directory (-b) download/extract/build in DIR; keep the
results
--optimize (-O) also compile with optimization: -O1 for
"python -O", -O2 for "python -OO", and -O0 to
disable [default: -O0]
--record filename in which to record list of installed
files
--always-unzip (-Z) don't install as a zipfile, no matter what
--site-dirs (-S) list of directories where .pth files work
--editable (-e) Install specified packages in editable form
--no-deps (-N) don't install dependencies
--allow-hosts (-H) pattern(s) that hostnames must match
--local-snapshots-ok (-l) allow building eggs from local checkouts
usage: easy_install-script.py [options] requirement_or_url ...
or: easy_install-script.py --help第3步：安裝libxml2
libxml2安裝，通過libxml2-python-2.7.7.win32-py2.7.exe安裝即可。安裝完這個以後，只是將相應的模塊解壓到了對應的目錄，並不能在Python編程中使用，還需要通過Easy Install來安裝一個lxml庫，它是一個C編寫的庫，能夠加速對HTML或XML的解析處理，詳細介紹可以參考（http://lxml.de/index.html）。安裝lxml需要使用Easy Install的執行腳本，例如我的腳本目錄爲E:\Program
Files\Python26\Scripts，執行安裝：
E:\Program Files\Python26\Scripts>easy_install lxml==2.2.2
可以看到安裝信息：
E:\Program Files\Python26\Scripts>easy_install lxml==2.2.2
Searching for lxml==2.2.2
Reading http://pypi.python.org/simple/lxml/
Reading http://codespeak.net/lxml
Best match: lxml 2.2.2
Downloading http://pypi.python.org/packages/2.6/l/lxml/lxml-2.2.2-py2.6-win32.egg#md5=dc73ae17e486037580371077efdc13e9
Processing lxml-2.2.2-py2.6-win32.egg
creating e:\program files\python26\lib\site-packages\lxml-2.2.2-py2.6-win32.egg
Extracting lxml-2.2.2-py2.6-win32.egg to e:\program files\python26\lib\site-packages
Adding lxml 2.2.2 to easy-install.pth file
Installed e:\program files\python26\lib\site-packages\lxml-2.2.2-py2.6-win32.egg
Processing dependencies for lxml==2.2.2
Finished processing dependencies for lxml==2.2.2使用XPath抽取
下面，我們使用XPath來實現網頁數據的抽取。這裏，我使用了一個Python的IDE工具——EasyEclipse for Python（Version: 1.3.1），可以直接創建Pydev Project，具體使用請查閱相關資料。
驗證可以使用XPath來定向抽取網頁數據，Python代碼如下：
import codecs
import sys
from lxml import etree
def readFile(file, decoding):
html = ''
try:
html = open(file).read().decode(decoding)
except:
pass
return html
def extract(file, decoding, xpath):
html = readFile(file, decoding)
tree = etree.HTML(html)
return tree.xpath(xpath)
if __name__ == '__main__':
sections = extract('peak.txt', 'utf-8', "//h3//a[@class='toc-backref']")
for title in sections:
print title.text首先，把網頁http://peak.telecommunity.com/DevCenter/EasyInstall的源代碼下載下來，存儲到文件peak.txt中，編碼UTF-8；
然後，在Python中讀取該文件內容，使用XPath抽取頁面上每個段落的標題內容，最後輸出到控制檯上，結果如下所示：
Troubleshooting
Windows Notes
Multiple Python Versions
Restricting Downloads with
Installing on Un-networked Machines
Packaging Others' Projects As Eggs
Creating your own Package Index
Password-Protected Sites
Controlling Build Options
Editing and Viewing Source Packages
Dealing with Installation Conflicts
Compressed Installation
Administrator Installation
Mac OS X "User" Installation
Creating a "Virtual" Python
"Traditional"
Backward Compatibility如果你足夠熟悉XPath，藉助於libxml2，你可以抽取網頁中任何你想要的內容。
