lxml is an efficient and easy-to-use library in Python for processing XML and HTML. It is built on top of the C libraries libxml2 and libxslt. When it comes to handling HTML documents, lxml uses a parser called html.parser that is part of its HTML module. This parser is quite lenient and designed to handle broken tags or bad syntax, similar to how web browsers process HTML.
When lxml encounters bad syntax or broken tags, it tries to make sense of the document as a web browser would, by repairing or adding missing tags and cleaning up the structure. This is particularly useful for scraping real-world web pages, which often do not have perfect HTML.
Here's how lxml can be used to parse a broken HTML document:
from lxml import html
broken_html = """
<html>
<head><title>Test</title>
<body>
<p>Paragraph one
<p>Paragraph two
<div>Div one without a closing tag
<p>Paragraph three
"""
# Use the HTML parser
tree = html.fromstring(broken_html)
# Print the fixed HTML
fixed_html = html.tostring(tree, pretty_print=True).decode('utf-8')
print(fixed_html)
In this example, lxml will automatically close the <p> and <div> tags. The output will be a well-formed HTML document:
<html>
<head><title>Test</title>
</head>
<body>
<p>Paragraph one</p>
<p>Paragraph two</p>
<div>Div one without a closing tag</div>
<p>Paragraph three</p>
</body>
</html>
lxml is particularly good at handling the following:
- Missing tags: If an element is missing a closing tag,
lxmlwill try to infer where it should be placed and add it automatically. - Misnested tags: When tags are not properly nested,
lxmlwill attempt to rearrange them to create a logical structure. - Unescaped characters:
lxmlwill handle unescaped characters in the HTML content, like&that should be written as&.
Remember, while lxml is good at cleaning up bad HTML, the resulting parse tree may not always match the original intention of the HTML document if the syntax errors are too severe. It's always best to start with well-formed HTML when possible. However, for scraping tasks where you have no control over the HTML quality, lxml's robustness is quite valuable.
