# 方法 如果没有合适过滤器,那么还可以定义一个方法,方法只接受一个元素参数[\[4\]](http://beautifulsoup.readthedocs.io/zh_CN/latest/#id91),如果这个方法返回`True`表示当前元素匹配并且被找到,如果不是则反回`False` 下面方法校验了当前元素,如果包含`class`属性却不包含`id`属性,那么将返回`True`: ``` def has_class_but_no_id(tag): return tag.has_attr('class') and not tag.has_attr('id') ``` 将这个方法作为参数传入`find_all()`方法,将得到所有\

标签: ``` soup.find_all(has_class_but_no_id) # [

The Dormouse's story

, #

Once upon a time there were...

, #

...

] ``` 返回结果中只有\

标签没有\标签,因为\标签还定义了”id”,没有返回\和\,因为\和\中没有定义”class”属性. 通过一个方法来过滤一类标签属性的时候, 这个方法的参数是要被过滤的属性的值, 而不是这个标签. 下面的例子是找出`href`属性不符合指定正则的`a`标签. ``` def not_lacie(href): return href and not re.compile("lacie").search(href) soup.find_all(href=not_lacie) # [Elsie, # Tillie] ``` 标签过滤方法可以使用复杂方法. 下面的例子可以过滤出前后都有文字的标签. ``` from bs4 import NavigableString def surrounded_by_strings(tag): return (isinstance(tag.next_element, NavigableString) and isinstance(tag.previous_element, NavigableString)) for tag in soup.find_all(surrounded_by_strings): print tag.name # p # a # a # a # p ``` 现在来了解一下搜索方法的细节 --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://jablack-programs.gitbook.io/python-notes/python-spider/beautifulsoup/sou-suo-wen-dang-shu/guo-lv-qi/fang-fa.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.