> Here we're using 'positional' to refer to parameters that PEP 362 calls "POSITIONAL_ONLY", whereas the regular TypeErrors (e.g. produced for user-defined functions) use 'positional' to mean what PEP 362 calls "POSITIONAL_OR_KEYWORD".

Here the error message is about "positional arguments," which are different from parameters.   (As you know, issue 15990 is to document this distinction in the glossary.)

Incidentally, it looks like the documentation for several of the functions in this part of the C API should probably be updated in this regard, for example:

http://docs.python.org/dev/c-api/arg.html#PyArg_UnpackTuple
http://docs.python.org/dev/c-api/arg.html#PyArg_ParseTuple

The PyArg_UnpackTuple documentation says, for example:

"A simpler form of parameter retrieval which does not use a format string to specify the types of the arguments. Functions which use this method to retrieve their parameters..."

The two occurrences of "parameter" here should be changed to "argument."