Python lxml模塊的基本使用方法分析
本文實(shí)例講述了Python lxml模塊的基本使用方法。分享給大家供大家參考，具體如下：
1 lxml的安裝
安裝方式：pip install lxml
2 lxml的使用
2.1 lxml模塊的入門使用
導(dǎo)入lxml 的 etree 庫 (導(dǎo)入沒有提示不代表不能用)
from lxml import etree
利用etree.HTML，將字符串轉(zhuǎn)化為Element對象,Element對象具有xpath的方法,返回結(jié)果的列表，能夠接受bytes類型的數(shù)據(jù)和str類型的數(shù)據(jù)
html = etree.HTML(text)
ret_list = html.xpath("xpath字符串")
把轉(zhuǎn)化后的element對象轉(zhuǎn)化為字符串，返回bytes類型結(jié)果 etree.tostring(element)
假設(shè)我們現(xiàn)有如下的html字符換，嘗試對他進(jìn)行操作
<div> <ul> <li class="item-1"><a href="link1.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >first item</a></li> <li class="item-1"><a href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >second item</a></li> <li class="item-inactive"><a href="link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li> <li class="item-1"><a href="link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li> <li class="item-0"><a href="link5.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a> # 注意，此處缺少一個 </li> 閉合標(biāo)簽 </ul> </div>
from lxml import etree
text = ''' <div> <ul>
<li class="item-1"><a href="link1.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >first item</a></li>
<li class="item-1"><a href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >second item</a></li>
<li class="item-inactive"><a href="link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>
<li class="item-1"><a href="link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>
<li class="item-0"><a href="link5.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a>
</ul> </div> '''
html = etree.HTML(text)
print(type(html))
handeled_html_str = etree.tostring(html).decode()
print(handeled_html_str)
輸出為
<class 'lxml.etree._Element'>
<html><body><div> <ul>
<li class="item-1"><a href="link1.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >first item</a></li>
<li class="item-1"><a href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >second item</a></li>
<li class="item-inactive"><a href="link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>
<li class="item-1"><a href="link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>
<li class="item-0"><a href="link5.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a>
</li></ul> </div> </body></html>
可以發(fā)現(xiàn)，lxml確實(shí)能夠把確實(shí)的標(biāo)簽補(bǔ)充完成，但是請注意lxml是人寫的，很多時候由于網(wǎng)頁不夠規(guī)范，或者是lxml的bug，即使參考url地址對應(yīng)的響應(yīng)去提取數(shù)據(jù)，任然獲取不到，這個時候我們需要使用etree.tostring的方法，觀察etree到底把html轉(zhuǎn)化成了什么樣子，即根據(jù)轉(zhuǎn)化后的html字符串去進(jìn)行數(shù)據(jù)的提取。
2.2 lxml的深入練習(xí)
接下來我們繼續(xù)操作，假設(shè)每個class為item-1的li標(biāo)簽是1條新聞數(shù)據(jù)，如何把這條新聞數(shù)據(jù)組成一個字典
from lxml import etree
text = ''' <div> <ul>
<li class="item-1"><a href="link1.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >first item</a></li>
<li class="item-1"><a href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >second item</a></li>
<li class="item-inactive"><a href="link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>
<li class="item-1"><a href="link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>
<li class="item-0"><a href="link5.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a>
</ul> </div> '''
html = etree.HTML(text)
#獲取href的列表和title的列表
href_list = html.xpath("http://li[@class='item-1']/a/@href")
title_list = html.xpath("http://li[@class='item-1']/a/text()")
#組裝成字典
for href in href_list:
item = {}
item["href"] = href
item["title"] = title_list[href_list.index(href)]
print(item)
輸出為
{'href': 'link1.html', 'title': 'first item'}
{'href': 'link2.html', 'title': 'second item'}
{'href': 'link4.html', 'title': 'fourth item'}
假設(shè)在某種情況下，某個新聞的href沒有，那么會怎樣呢？
from lxml import etree
text = ''' <div> <ul>
<li class="item-1"><a>first item</a></li>
<li class="item-1"><a href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >second item</a></li>
<li class="item-inactive"><a href="link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>
<li class="item-1"><a href="link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>
<li class="item-0"><a href="link5.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a>
</ul> </div> '''
結(jié)果是
{'href': 'link2.html', 'title': 'first item'}
{'href': 'link4.html', 'title': 'second item'}
數(shù)據(jù)的對應(yīng)全部錯了，這不是我們想要的，接下來通過2.3小節(jié)的學(xué)習(xí)來解決這個問題
2.3 lxml模塊的進(jìn)階使用
前面我們?nèi)〉綄傩?，或者是文本的時候，返回字符串 但是如果我們?nèi)〉降氖且粋€節(jié)點(diǎn)，返回什么呢?
返回的是element對象，可以繼續(xù)使用xpath方法，對此我們可以在后面的數(shù)據(jù)提取過程中：先根據(jù)某個標(biāo)簽進(jìn)行分組，分組之后再進(jìn)行數(shù)據(jù)的提取
示例如下：
from lxml import etree
text = ''' <div> <ul>
<li class="item-1"><a>first item</a></li>
<li class="item-1"><a href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >second item</a></li>
<li class="item-inactive"><a href="link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>
<li class="item-1"><a href="link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>
<li class="item-0"><a href="link5.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a>
</ul> </div> '''
html = etree.HTML(text)
li_list = html.xpath("http://li[@class='item-1']")
print(li_list)
結(jié)果為：
[<Element li at 0x11106cb48>, <Element li at 0x11106cb88>, <Element li at 0x11106cbc8>]
可以發(fā)現(xiàn)結(jié)果是一個element對象，這個對象能夠繼續(xù)使用xpath方法
先根據(jù)li標(biāo)簽進(jìn)行分組，之后再進(jìn)行數(shù)據(jù)的提取
from lxml import etree
text = ''' <div> <ul>
<li class="item-1"><a>first item</a></li>
<li class="item-1"><a href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >second item</a></li>
<li class="item-inactive"><a href="link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>
<li class="item-1"><a href="link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>
<li class="item-0"><a href="link5.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a>
</ul> </div> '''
#根據(jù)li標(biāo)簽進(jìn)行分組
html = etree.HTML(text)
li_list = html.xpath("http://li[@class='item-1']")
#在每一組中繼續(xù)進(jìn)行數(shù)據(jù)的提取
for li in li_list:
item = {}
item["href"] = li.xpath("./a/@href")[0] if len(li.xpath("./a/@href"))>0 else None
item["title"] = li.xpath("./a/text()")[0] if len(li.xpath("./a/text()"))>0 else None
print(item)
結(jié)果是：
{'href': None, 'title': 'first item'}
{'href': 'link2.html', 'title': 'second item'}
{'href': 'link4.html', 'title': 'fourth item'}
前面的代碼中，進(jìn)行數(shù)據(jù)提取需要判斷，可能某些一面不存在數(shù)據(jù)的情況，對應(yīng)的可以使用三元運(yùn)算符來解決
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希望本文所述對大家Python程序設(shè)計(jì)有所幫助。
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