BeautifulSoup复方类名称搜索时返回空列表 [英] BeautifulSoup returns empty list when searching by compound class names

问题描述

BeautifulSoup使用正则表达式由复合类名称搜索时返回空列表。

BeautifulSoup returns empty list when searching by compound class names using regex.

例如：

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*)$"))

我需要的类选择是非常precise。任何想法？

I need the class selection to be very precise. Any ideas?

推荐答案

不幸的是，当您试图使在包含多个类的类属性值的常规前pression比赛， BeautifulSoup 将分别应用常规的前pression到每一个班级。以下是有关该问题的相关内容：

Unfortunately, when you try to make a regular expression match on a class attribute value that contains multiple classes, BeautifulSoup would apply the regular expression to every single class separately. Here are the relevant topics about the problem:

• Python常规的前pression为美丽的汤


• 多个CSS类搜索是不方便

• Python regular expression for Beautiful Soup
• Multiple CSS class search is unhandy

这一切都是因为 类是一个很特别的多值属性以及每次解析HTML时， BeautifulSoup 的树建设者之一（根据解析器选择）内部将一个类的字符串值入类（从 HTMLTreeBuilder 的文档字符串引号）的列表：

This is all because class is a very special multi-valued attribute and every time you parse HTML, one of the BeautifulSoup's tree builders (depending on the parser choice) internally splits a class string value into a list of classes (quote from the HTMLTreeBuilder's 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，但这里是一个黑客十岁上下一 - 我们要问 BeautifulSoup 不办理类：由我们制作简单的自定义树构建一个多值属性：

---

There are multiple workarounds, but here is a hack-ish one - we are going to ask BeautifulSoup not to handle class as a multi-valued attribute by making our simple custom tree builder:

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，常规的前pression将被应用到类属性值作为一个整体。

In this case the regular expression would be applied to a class attribute value as a whole.

另外，你可以只用解析 XML 的HTML功能启用（如果适用）：

Alternatively, you can just parse the HTML with xml features enabled (if this is applicable):

soup = BeautifulSoup(data, "xml")

---

您也可以使用 CSS选择器并匹配所有

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

如果需要的话

您可以手动应用常规的前pression：

You can then apply the regular expression manually if needed:

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)

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