I don't think it worth to add support of keyword for the first mandatory argument. This can freeze the poor and inconsistent () names. For example compress()/decompress() methods of bz2 and lzma objects doesn't support keyword arguments. And why you use "string" name for decompress() argument?

Renaming of "memLevel" argument to "memlevel" is not backward compatible and can break third-part code (if anyone use it). This may require starting of deprecation process. Difference between a code and a documentation is a bug and should be fixed for all Python versions.

Note, that calling a function with keyword arguments is a little slower (a lot of slower for fast functions) than calling a function with positional-only arguments.