I have a directory full (~103, 104) of XML files from which I need to extract the contents of several fields. 
I've tested different xml parsers, and since I don't need to validate the contents (expensive) I was thinking of simply using xml.parsers.expat (the fastest one) to go through the files, one by one to extract the data. 

Is there a more efficient way? (simple text matching doesn't work)
Do I need to issue a new ParserCreate() for each new file (or string) or can I reuse the same one for every file?
Any caveats?

Thanks!
If you know that the XML files are generated using the ever-same algorithm, it might be more efficient to not do any XML parsing at all. E.g. if you know that the data is in lines 3, 4, and 5, you might read through the file line-by-line, and then use regular expressions.
Of course, that approach would fail if the files are not machine-generated, or originate from different generators, or if the generator changes over time. However, I'm optimistic that it would be more efficient.
Whether or not you recycle the parser objects is largely irrelevant. Many more objects will get created, so a single parser object doesn't really count much.
What is the most efficient way of extracting information from a large number of xml files in python?