Argument Clinic: support for simple expressions?

[birkenfeld]

BPO	20226
Nosy	@birkenfeld, @larryhastings, @meadori, @zware, @serhiy-storchaka
Files	larry.clinic.rollup.patch.two.diff.1.txt larry.clinic.rollup.patch.two.diff.2.txt larry.clinic.rollup.patch.two.diff.3.txt larry.clinic.rollup.patch.two.diff.4.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 2014-01-16.19:33:41.897>
created_at = <Date 2014-01-12.10:29:49.464>
labels = ['type-feature']
title = 'Argument Clinic: support for simple expressions?'
updated_at = <Date 2014-01-26.04:48:06.172>
user = 'https://github.com/birkenfeld'

bugs.python.org fields:

activity = <Date 2014-01-26.04:48:06.172>
actor = 'larry'
assignee = 'larry'
closed = True
closed_date = <Date 2014-01-16.19:33:41.897>
closer = 'larry'
components = []
creation = <Date 2014-01-12.10:29:49.464>
creator = 'georg.brandl'
dependencies = []
files = ['33473', '33492', '33499', '33500']
hgrepos = []
issue_num = 20226
keywords = []
message_count = 24.0
messages = ['207946', '207947', '207956', '207957', '208135', '208139', '208175', '208176', '208177', '208178', '208253', '208254', '208255', '208259', '208260', '208266', '208288', '208290', '208291', '208292', '208293', '208302', '208303', '208314']
nosy_count = 6.0
nosy_names = ['georg.brandl', 'larry', 'meador.inge', '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/issue20226'
versions = ['Python 3.4']

[birkenfeld]

Take for example select.epoll.__new__():

static PyObject *
pyepoll_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
 int flags = 0, sizehint = FD_SETSIZE - 1;
 static char *kwlist[] = {"sizehint", "flags", NULL};

 if (!PyArg_ParseTupleAndKeywords(args, kwds, "|ii:epoll", kwlist,
 &sizehint, &flags))
 return NULL;

How should that be handled? Currently I can't specify FD_SETSIZE - 1 as the default value, but I don't want a magic -909 either :)

[serhiy-storchaka]

See also a discussion in bpo-20193. zlib needs this in many functions.

[larryhastings]

Yes, this is supported, just undocumented (for now). The magic you want is, for example in Modules/_sre.c:

endpos: Py_ssize_t(c_default="PY_SSIZE_T_MAX") = sys.maxsize

[birkenfeld]

Nice, thanks.

[larryhastings]

The attached patch extends Argument Clinic and the inspect module: now you may use simple (!) expressions as default values. So for example "sys.maxsize - 1" should now work fine.

• Names may be in the current module; as a backup they will also be looked up in sys.modules.
• You may look up attributes of names.
• You may subscript into names.
• You may use math operators, both unary and binary.
• int/float/string literals are (still) fine.
• You may not use: function calls, list/set/dict/tuple/bytes literals, generator expressions or comprehensions, if expressions, anything fun.

Other changes in this diff:

• "doc_default" is gone, it no longer makes sense.
• "py_default" and "c_default" handling is simpler and more predictable.
• Minor doc fix suggested on tracker.

The docs still need work. More tests would be good too but I'm already overwhelmed by work--could one of you guys contribute some tests?

[meadori]

Larry, nice. I am verified that your latest patch fixes my third sqlite3
nit from bpo-20178.

[zware]

Just confirmed that this patch fixes the traceback I was getting from winreg in bpo-20172, but this has a new oddity:

>>> help(winreg)
...
 ConnectRegistry(computer_name=<object object at 0x0190E148>, key=<object object at 0x0190E148>)
...

Every param of every function has this kind of thing, positional or keyword, default or no. I'll try to look into it, but my hopes aren't high (much of clinic's inner workings are still mysterious to me).

[larryhastings]

That's okay, email me a sample at

larry at hastings dot org

and I'll take a look at it. Be sure to tell me which patch(es) were applied at the time.

(Note: all you need to send is the Clinic block.)

[zware]

Actually, I can reproduce on tip with just this patch applied; os.chmod shows it. And I was wrong, params that have a default are correct, it's just ones without.

[larryhastings]

I'd prefer it if you emailed me as I asked. That will help me get to it a lot quicker.

[larryhastings]

Okay, I have a fix for the help(os.chmod) problem, that'll be in the next refreshed patch.

[serhiy-storchaka]

Why not allow arbitrary string as py_default?

[larryhastings]

Isn't that what it does?

I may actually remove py_default. Nobody uses it, and I don't think you need it--you just specify what you want as the real default value.