Issue 20401: inspect.signature removes initial starred method params (bug)

>>> import inspect
>>> class C:
	def meth(*args): pass
	
>>> str(inspect.signature(C.meth))
'(*args)'
>>> c=C()
>>> str(s=inspect.signature(c.meth))
'()'

*args should have been left in even for the bound method, as idlelib calltips do.
Since '*' is not a word character,
idlelib.Calltips._first_param = re.compile('(?<=\()\w*\,?\s*')
does not see '*args' as a substring to be deleted with
    argspec = _first_param.sub("", argspec)

The same comment applies to
    def meth2(**kwds): pass
even though calling the bound method would fail.

Yury, can you look in to this?

I have been modifying inspect.signature, but (almost) exclusively in from_builtin.  If this is my fault I'll be happy to fix it.

There does not appear to be a test for this. If so, this case may not have ever worked right. Here is the only failure at the moment (which should also be fixed).

F:\Python\dev>4\py34\pcbuild\python_d.exe -m test test_inspect
[1/1] test_inspect
test test_inspect failed -- Traceback (most recent call last):
  File "F:\Python\dev\4\py34\lib\test\test_inspect.py", line 1623, in test_signature_on_builtins
    test_callable(type)
  File "F:\Python\dev\4\py34\lib\test\test_inspect.py", line 1604, in test_callable
    signature = inspect.signature(o)
  File "F:\Python\dev\4\py34\lib\inspect.py", line 1555, in signature
    raise ValueError('callable {!r} is not supported by signature'.format(obj))
ValueError: callable <class 'type'> is not supported by signature

I just tried it in 3.3 (3.3.1rc1) and it had the same problem.

Yes, that's s bug. I'll take a look tomorrow.

Sorry, I should have said that I tried repository versions of both 3.3 and 3.4.

Patch is attached, please review.
Should we commit this to 3.3 too?

New changeset 3544827d42e6 by Yury Selivanov in branch 'default':
inspect.signature: Handle bound methods with '(*args)' signature correctly #20401
http://hg.python.org/cpython/rev/3544827d42e6

Committed. Thank you, Terry.

Is there any reason that the second case Terry provide still will failed with ValueError?

class C:
    def meth2(**kwds): pass


ip.signature(C().meth2)

Traceback (most recent call last):
  File "/home/linux/Python/cpython/Lib/idlelib/idle_test/test_calltips.py", line 139, in test_starred_parameter
    self.assertEqual(signature(meth), mtip)
  File "/home/linux/Python/cpython/Lib/idlelib/calltips.py", line 149, in get_argspec
    argspec = str(inspect.signature(fob))
  File "/home/linux/Python/cpython/Lib/inspect.py", line 3028, in signature
    return Signature.from_callable(obj, follow_wrapped=follow_wrapped)
  File "/home/linux/Python/cpython/Lib/inspect.py", line 2778, in from_callable
    follow_wrapper_chains=follow_wrapped)
  File "/home/linux/Python/cpython/Lib/inspect.py", line 2195, in _signature_from_callable
    return _signature_bound_method(sig)
  File "/home/linux/Python/cpython/Lib/inspect.py", line 1785, in _signature_bound_method
    raise ValueError('invalid method signature')
ValueError: invalid method signature

> Is there any reason that the second case Terry provide still will failed with ValueError?

> class C:
>    def meth2(**kwds): pass


> ip.signature(C().meth2)

Yes, the reason is that `C().meth2` is an invalid method that can't be called. Try calling `C().meth2()` and you will get a TypeError.

There is no bug here.

OK, we will change this example in test_calltips once calltips uses .signature (#19903).

nosy: + ncoghlan
messages: + msg209488

assignee: yselivanov
keywords: + patch