[Python-Dev] New policies for the Derby -- please read!
larry at hastings.org
Sat Jan 25 13:19:18 CET 2014
1) New policy for what can and cannot be converted during the Derby
First, let me apologize for only figuring this out now. The Derby has
been a learning process, discovering things that Argument Clinic didn't
handle. And there were a lot of funny edge cases that we weren't going
to discover until we tried doing the conversion. And to be honest I was
pushing harder than I should have.
The new policy for conversion work for Python 3.4:
We may only convert functions that have signatures that we can
represent 100% accurately in an inspect.Signature object.
IF the function has a default value that can't be represented in
Python (e.g. NULL), but we can find a value in Python that behaves
identically to not passing in that parameter (e.g. _sha1.sha1(b'')
== _sha1.sha1()), then we may convert that function using that
clever default value (e.g. "string: object(c_default='NULL') = b'' ").
IF the function has parameters with default values that are dynamic
or cannot be represented accurately in Python, it cannot be
converted without changing its semantics. So it cannot be converted
IF the function *requires* "optional groups" (as in, the original
function used switch(PyTuple_GET_SIZE(args)) and multiple calls to
PyArg_ParseTuple()), then it's permissible to convert it for 3.4,
but they are low priority. Such functions have semantics that are
so weird, we will have to modify inspect.Parameter to support them,
and that will only happen in 3.5. However, I will ensure that they
otherwise convert correctly for 3.4. (They won't actually generate
signatures. They will however generate the first line of the
For 3.5, I expect we'll have more leeway in doing things like "this
should accept an int or None". But we should talk about that then.
If you have patches outstanding that convert functions that shouldn't be
converted for 3.4, please put them aside. We can almost certainly use
them for 3.5.
If any conversions have been committed that change the semantics of the
function, someone will have to back them out. I'd appreciate it if the
person who checked it in could do it. I expect to make a pass before
rc1 to check all the conversions myself. (Which I hope will be quite
time-consuming, as hopefully there will be lots of converted functions
2) New recommendation for marking to-do functions
If you examine a function and determine that it can't be converted to
Argument Clinic right now, please add a comment to that effect. The
comment should be one line, and contain a special marker so we can find
it easily with searches.
I nominate two different markers:
"AC 3.4" means "It's okay to convert this function to Argument Clinic
in 3.4, but it can't be converted right now because of a bug or missing
feature in Argument Clinic."
"AC 3.5" means "This function can't be converted to Argument Clinic in
3.4, it must wait for 3.5."
I encourage you to add a little text saying why, like:
/* AC 3.4: waiting for *args support */
/* AC 3.5: value parameter has default value of NULL */
Finally, I've realized that right now there's no good way to stay
abreast of what's new and changing in clinic.py. I check in a patch
just about every day for clinic.py, and sometimes I don't remember to
update the "howto". The best way unfortunately is to read the output of
If you have questions, you can email me directly at "larry at hastings
dot org", or you can find me in the #python-dev IRC channel.
Thank you, everybody who's participating in the Derby, and again I'm
sorry I didn't realize sooner this *had* to be the policy for 3.4.
Hope to see your issues in the tracker,
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