I've read in lots of formats, including many XML and binary files. 99% of the time there is a library that already handles the low-level interaction with those

I've read in lots of formats, including many XML and binary files. 99% of the time there is a library that already handles the low-level interaction with those files. The only times I've had to write original Python code that reads files directly have typically been things that could be processed line by line (eg various record-based data formats). I'm trying to think of a counter example but I'm coming up blank.