一尘不染

通过复合类名称搜索时,BeautifulSoup返回空列表

python

当使用正则表达式按复合类名称搜索时,BeautifulSoup返回空列表。

例:

import re
from bs4 import BeautifulSoup

bs = 
    """
    <a class="name-single name692" href="www.example.com"">Example Text</a>
    """

bsObj = BeautifulSoup(bs)

# this returns the class
found_elements = bsObj.find_all("a", class_= re.compile("^(name-single.*)$"))

# this returns an empty list
found_elements = bsObj.find_all("a", class_= re.compile("^(name-single name\d*)$"))

我需要对课程的选择非常精确。有任何想法吗?


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2020-12-20

共1个答案

一尘不染

不幸的是,当您尝试对包含多个类的类属性值进行正则表达式匹配时,BeautifulSoup会将正则表达式分别应用于每个单个类。

这一切都是因为class是一个很特别的多值属性,每一次你解析HTML的一个BeautifulSoup的树建设者(取决于解析器选择)内部分裂从一个类的字符串值入类(报价列表HTMLTreeBuilder的docstring):

# The HTML standard defines these attributes as containing a
# space-separated list of values, not a single value. That is,
# class="foo bar" means that the 'class' attribute has two values,
# 'foo' and 'bar', not the single value 'foo bar'.  When we
# encounter one of these attributes, we will parse its value into
# a list of values if possible. Upon output, the list will be
# converted back into a string.

有多种解决方法,但这是一种hack-ish解决方案-
我们将通过制作简单的自定义树生成器来要求BeautifulSoup不要将其class作为多值属性来处理:

import re

from bs4 import BeautifulSoup
from bs4.builder._htmlparser import HTMLParserTreeBuilder


class MyBuilder(HTMLParserTreeBuilder):
    def __init__(self):
        super(MyBuilder, self).__init__()

        # BeautifulSoup, please don't treat "class" specially
        self.cdata_list_attributes["*"].remove("class")


bs = """<a class="name-single name692" href="www.example.com"">Example Text</a>"""
bsObj = BeautifulSoup(bs, "html.parser", builder=MyBuilder())
found_elements = bsObj.find_all("a", class_=re.compile(r"^name\-single name\d+$"))

print(found_elements)

在这种情况下,正则表达式将class整体应用于属性值。


或者,您可以仅分析xml启用了功能的HTML (如果适用):

soup = BeautifulSoup(data, "xml")

您还可以使用CSS选择器,将所有元素与name-singleclass和以“ name”开头的类进行匹配:

soup.select("a.name-single,a[class^=name]")

然后,您可以根据需要手动应用正则表达式:

pattern = re.compile(r"^name-single name\d+$")
for elm in bsObj.select("a.name-single,a[class^=name]"):
    match = pattern.match(" ".join(elm["class"]))
    if match:
        print(elm)
2020-12-20