Argument Clinic: add support for __init__

@larryhastings

BPO	20294
Nosy	@larryhastings, @zware, @serhiy-storchaka
Files	larry.argument.clinic.init.and.new.patch.1.txt larry.argument.clinic.init.and.new.patch.2.txt

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/larryhastings'
closed_at = <Date 2014-01-19.07:51:59.784>
created_at = <Date 2014-01-18.11:43:26.038>
labels = ['type-feature']
title = 'Argument Clinic: add support for __init__'
updated_at = <Date 2014-01-22.03:13:07.590>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2014-01-22.03:13:07.590>
actor = 'larry'
assignee = 'larry'
closed = True
closed_date = <Date 2014-01-19.07:51:59.784>
closer = 'larry'
components = ['Demos and Tools']
creation = <Date 2014-01-18.11:43:26.038>
creator = 'serhiy.storchaka'
dependencies = []
files = ['33537', '33542']
hgrepos = []
issue_num = 20294
keywords = []
message_count = 13.0
messages = ['208395', '208406', '208412', '208413', '208444', '208451', '208453', '208458', '208459', '208460', '208461', '208497', '208739']
nosy_count = 5.0
nosy_names = ['larry', 'rmsr', 'python-dev', 'zach.ware', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue20294'
versions = ['Python 3.4']

Currently Argument Clinic doesn't support the __init__ methods, mainly because the C implementation of this method should return int, not PyObject *. In some cases it is possible to wrap a function generated by Argument Clinic (as in Modules/_pickle.c). But not always, because the __init__ method is called with the self, args, and kwargs arguments, while Argument Clinic can generate function without kwargs.

Oh! I thought it worked fine, because I've seen people convert both an __init__ and a __new__. But I guess they wrapped them.

It's an easy change, I can try to do that today.

As is probably expected, __init__ and __call__ procs
can't be converted.

I should have a fix in for __init__ and __call__ later today. (Issue bpo-20294.)
For the record, you could convert them, you just had to wrap the parsing function
to deal with the return type difference, and *args / **kwargs might be tricky too.

* sqlite3.Connection.{execute, executemany, executescript} don't use
  PyArg_Parse*.

In the next few days I'm going to add support for "*args" and "**kwargs", and
then you'll be able to convert these functions. (Issue bpo-20291.) Again, even
if Argument Clinic doesn't do any parsing, it's still helpful to have it
generate signatures.

* The clinic version of 'sqlite3.adapt' has an argument string of "O|OO".
  The first optional parameter defaults to 'pysqlite_PrepareProtocolType'
  in C and 'sqlite3.ProtocolType' in Python.  However, I don't know how to
  represent the Python value because Python default values are 'eval'd by
  clinic \*and* the 'sqlite3' module is not imported for the eval.

You'll be able to do this soon:

parameter: object(c_default='pysqlite_PrepareProtocolType') = ProtocolType

This feature isn't checked in yet, I'm waiting for a review. It's part of
bpo-20226, which I guess you already noticed.

The clinic version of 'sqlite3.Cursor.fetchmany' has an arguments string
of "|i". The first parameter defaults to
'((pysqlite_Cursor *)self)->arraysize' in C and 'self.arraysize' in
Python. I don't know how to express the Python initialization.

You can't. How about you use a default of -1 and then:

if (maxrows == -1)
maxrows = self->arraysize

I didn't convert 'sqlite3.Cursor.setinputsizes' and
'sqlite3.Cursor.setoutputsize' because they share a docstring and
simple no-op method def.

I'd prefer it if you converted them anyway. Converting them means they'll
have signature information which is an unconditional good.

I didn't convert 'sqlite.connect' because it would have required
packaing the arguments back up to pass to 'PyObject_Call'.

Once I add the ability to pass in *args and **kwargs, you'll be able to
convert sqlite.connect.

I think I responded to all your other comments when I reviewed the patch.

Thanks!

Oops, sorry, that last comment was intended for a different issue. Please ignore, and sorry for the spam!

Here's a patch. Wasn't as easy as I thought, it kind of took all day.

Changes include:

__init__ and __new__ always take kwargs.
- if the function signature doesn't accept keyword arguments,
  it calls _PyArg_NoKeywords().
__init__ returns int, not PyObject *.
__init__ and __new__ should support all argument parsing
scenarios (unpack tuple, positional only, etc).

Pre-exiting behavior:

The C function basename chosen for __new__ is just the name of
the class, it doesn't end in __new__.
The methoddef #define is suppressed.

Rietveld doesn't like the patch and I'm having a hard time finding a changeset on which I can get it to apply cleanly. May I suggest avoiding --git on hg diff unless copying/moving/renaming a file?

Whoops, that doesn't apply cleanly. Here's an updated patch.

Output looks good and I didn't see anything that scared me in the patch, though I can't pretend to fully understand 100% of it. Builds on Windows, pickle tests pass, and nothing else is affected (that's checked in so far). Looks good to me, as far as I can see.

I have reviewed this as best I am able. I'll be honest that a lot of clinic.py makes my eyes cross; I'm used to webdev templating, which is inverted from AC (flow control inside the template). Not complaining, it's a complicated subject. I do like the centralization of the templates.

I didn't see anything that jumped out at me. I tried out the new conversions on socketmodule and like the output, and none of the existing conversions mutated. So LGTM!

It took me a while to figure out how to make __new__ a class method though, decorator support should probably be documented (or else a hint like '__new__ must be a @classmethod!')

New changeset 2e32462e4832 by Larry Hastings in branch 'default':
Issue bpo-20294: Argument Clinic now supports argument parsing for __new__ and
http://hg.python.org/cpython/rev/2e32462e4832

Checked in. Thanks for bringing the problem to my attention, Serhiy, and thanks for the reviews you two!

rmsr: If I had a stronger background in templating, maybe Argument Clinic would be cleaner inside. As it is I'm beating the problem to death with sheer force of will.

Thank you Larry, now I can use Argument Clinic in the __init__ methods. But there is one problem.

Docstring generated for the __init__ method contains the "__init__" name in the signature. Therefore it can't be used as class docstring. On other hand, the compiler complains of not used __init__ docstring.

That problem will be irrelevant, once builtin classes support signatures (bpo-20189).

Issue #20294: Argument Clinic now supports argument parsing for __new…

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Argument Clinic: add support for init #64493

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serhiy-storchaka commented on Jan 18, 2014

larryhastings commented on Jan 18, 2014

larryhastings commented on Jan 18, 2014

larryhastings commented on Jan 18, 2014

larryhastings commented on Jan 19, 2014

zware commented on Jan 19, 2014

larryhastings commented on Jan 19, 2014

zware commented on Jan 19, 2014

rmsr commented on Jan 19, 2014

python-dev commented on Jan 19, 2014

larryhastings commented on Jan 19, 2014

serhiy-storchaka commented on Jan 19, 2014

larryhastings commented on Jan 22, 2014

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Argument Clinic: add support for init #64493