Clinic fixes: add converters with length, version directive, "self converter"

[larryhastings]

BPO	19730
Nosy	@brettcannon, @ncoghlan, @pitrou, @larryhastings
Files	larry.misc.clinic.fixes.diff.1.patch larry.misc.clinic.fixes.diff.3.patch

^{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 2013-11-23.22:54:56.541>
created_at = <Date 2013-11-23.02:28:12.286>
labels = ['type-bug', 'build']
title = 'Clinic fixes: add converters with length, version directive, "self converter"'
updated_at = <Date 2013-11-23.22:54:56.540>
user = 'https://github.com/larryhastings'

bugs.python.org fields:

activity = <Date 2013-11-23.22:54:56.540>
actor = 'larry'
assignee = 'larry'
closed = True
closed_date = <Date 2013-11-23.22:54:56.541>
closer = 'larry'
components = ['Build']
creation = <Date 2013-11-23.02:28:12.286>
creator = 'larry'
dependencies = []
files = ['32790', '32814']
hgrepos = []
issue_num = 19730
keywords = ['patch']
message_count = 5.0
messages = ['203958', '204016', '204036', '204115', '204124']
nosy_count = 5.0
nosy_names = ['brett.cannon', 'ncoghlan', 'pitrou', 'larry', 'python-dev']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue19730'
versions = ['Python 3.4']

[larryhastings]

Two minor changes for Argument Clinic.

• Added a "version" directive, so a programmer can require a
  specific version (or better) of Clinic.

• Finished off support for all the 'legacy' converters. The ones today
  were those that give off a "length" parameter. This was complicated
  by finally dealing properly with the Py_buffer conversion stuff.

To properly handle length parameters, I had to support PY_SSIZE_T_CLEAN being turned off (when are we gonna throw that away?). So I added a new type to pyports.h, Py_ssize_clean_t, which is either an int or a Py_ssize_t depending on PY_SSIZE_T_CLEAN.

I've run out of gas and am going to bed. I know I have two TODO items in the diff so far; I'll deal with those tomorrow. But can I get a quick review of the rest, so I can get this in tomorrow?

[pitrou]

Argument Clinic is an internal tool, so I don't think it's bound by the feature freeze.
(and, besides, you are the RM :-))

[ncoghlan]

+1 to what Antoine said - keeping the initial iteration internal only
actually buys us some time :)

[larryhastings]

Attached is a fresh patch. I added a third new feature: the "self converter", which allows you to change the type of (or rename) self. For an example of its use, check out dbm.dbm.get in Modules/_dbmmodule.c.

[python-dev]

New changeset 760ccd78e874 by Larry Hastings in branch 'default':
Issue bpo-19730: Argument Clinic now supports all the existing PyArg
http://hg.python.org/cpython/rev/760ccd78e874