On Wed, Jun 24, 2020 at 7:40 AM Ethan Furman <ethan@stoneleaf.us> wrote:
Okay, I took Paul Moore's advice and went looking in existing code for some examples, and came across the following:

if isinstance(v, int):
# v is an offset
elif isinstance(v, str):
# v is a docstring
elif isinstance(v, tuple) and len(v) in (2, 3) and isinstance(v[0], baseinteger) and isinstance(v[1], (basestring, NoneType)):
# v is an offset, a docstring, and (maybe) a default
elif isinstance(v, tuple) and len(v) in (1, 2) and isinstance(v[0], (basestring, NoneType)):
# v is a docstring and (maybe) a default

That seems like it would be a perfect match (hah) for the new syntax, but I am not confident in my efforts.

This is what I started with:

match v:  # goal here is to turn v into an (offset, docstring, default value)
case int:
v = v, None, None
case str:
v = None, v, None
case (str, ):
# how to combine with above case?
v = None, v[0], None
case (int, str):
v += (None, )
case (int, str, default):
pass
case (str, default):
v = None, v[0], v[1]

Which got me to here:

match v:  # goal here is to turn v into an (offset, docstring, default value)
case int(offset):
v = offset, None, None
case str(doc) | (str(doc), ):
v = None, doc, None
case (int(offset), str(doc)):
v = offset, doc, None
case (int(offset), str(doc), default):
pass
case (str(doc), default):
v = None, doc, default

Is this correct?

Yes.

Side note: I would much rather read "case str(doc) or (str(doc), )" instead of a |.

Duly noted, we'll come back to this.

--
--Guido van Rossum (python.org/~guido)