lxml VS html5lib

lxml

Parsel is a library build to extract data from XML/HTML documents with XPath and CSS selectors support, and could be combined with regular expressions. It's usees lxml parser under the hood by default.

So, now that I no longer work in that industry, and I had some free time, I created a lazy parsing package using lxml instead of the xml parser in the standard library, which can help people who want to have a python only parsing solution.

I got curious about this now so I did some tests on my own, and it appears that the XML parser implementation in Python does indeed strip all newline characters from attributes. Whether this is according to XML standard I do not know; I also briefly tried an alternative XML implementation for Python and it behaves the same, so I would assume that this is standard behavior, but I'm not knowledgable enough about XML to say for certain.

I use lxml for the XML parsing and pyodbc as the ODBC library. We have a small team so I just keep it as simple as possible: 1. A cursor yields the XML documents from a SQL query as a stream 2. A generator function parses the XML document and yields the rows (you could parallelize this step) 3. Stream each of the resulting rows to a single CSV file 4. Scoop up the resulting CSV file into the target database (usually with the DB engine's loader; bulk insert isn't so fast over ODBC) It ends up being a straight forward, low-overhead approach.

Generally, I'm already using Python to glue together things like OpenCV or libxml, which do the heavy-lifting, and taking advantage of how things like Qt's QImage release Python's Global Interpreter Lock, allowing me to load and process images on a background thread, so the Python code itself is usually already I/O-bound, but yes. If the Python code would become a bottleneck, it helps with that too.

lxml is an XML parser however, it also supports HTML parsing. It's blazing fast and supports XPath. I think it isn't as beginner friendly to use, though it has detailed documentation. It works less well with heavily broken HTML documents and the encoding detection isn't as good as the one of BS4.

According to lxml benchmarking docs, Python’s built in xml parser wouldn’t behave that bad either: https://github.com/lxml/lxml/blob/master/doc/performance.txt

Neither did html5lib.

Easier example...sphinx is a document generator for python programs (creating docs for the API of programs from source-code comments for example). Spinx depends on html5lib which itself again depends on six...want to make a guess what six uses to generate its API docs? ;) So if you want the api docs of six you will have to first install it without to be able to get a working sphinx install then redo the six on including the building of the API docs.