One wrinkle of PEP 362 in CPython is callables implemented directly in
C. Right now there's no good way to generate such signatures
automatically. That's why we kept __signature__ in the spec, to allow
implementors to generate signatures by hand for these callables.
But the wrinkle gets wrinklier. The problem is, you often can't add
arbitrary attributes to these objects:
>>> import os
>>> os.stat.random_new_attribute = 3
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'builtin_function_or_method' object has no attribute
'random_new_attribute'
If users are to attach precomputed signatures to callables implemented
in C, those callables may need to *already* have a __signature__ attribute.
I've already added __signature__ to PyCFunctionObject in the PEP 362
patch. This takes care of the vast bulk of such callables. But there
are a bunch of obscure callable objects in CPython, and I suspect some
of them may need a __signature__ attribute.
Here's an almost- complete list, listed as their Python type:
functools.KeyWrapper (result of functools.cmp_to_key)
weakref.weakref
method (bound method objects, aka "x = Class(); x.method")
instancemethod (is this still even used? it's never used in trunk)
operator.itemgetter
operator.attrgetter
operator.methodcaller
_json.Scanner (result of _json.make_scanner)
_json.Encoder (result of _json.make_encoder)
_ctypes.DictRemover (I'm not even sure how you can get your hands on
one of these)
sqlite3.Connection
I produced this by grepping for "/* tp_call */" and ignoring all of them
that were set to "0", then creating one of those objects and trying (and
failing) to set a __signature__ attribute.
There are four more candidates I found with the grep but couldn't figure
out how to instantiate and test. They have to do with the descriptor
protocol, aka properties, but the types aren't directly exposed by
Python. They're all defined in Object/descrobject.c. The internal
class names are:
method_descriptor
classmethod_descriptor
wrapper_descriptor
method-wrapper (you get one of these out of a "wrapper_descriptor")
I'm happy to do the work, but I don't have a good sense of which
callables need a __signature__ attribute. Can someone here tell me
which ones might need a __signature__ attribute?
//arry/
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