inspect.signature removes initial starred method params (bug)

[terryjreedy]

BPO	20401
Nosy	@terryjreedy, @ncoghlan, @larryhastings, @1st1, @mlouielu
Files	signature_method_first_arg_01.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/1st1'
closed_at = <Date 2014-01-28.17:27:33.930>
created_at = <Date 2014-01-27.02:16:33.088>
labels = ['type-bug']
title = 'inspect.signature removes initial starred method params (bug)'
updated_at = <Date 2017-05-02.02:22:59.304>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2017-05-02.02:22:59.304>
actor = 'terry.reedy'
assignee = 'yselivanov'
closed = True
closed_date = <Date 2014-01-28.17:27:33.930>
closer = 'yselivanov'
components = []
creation = <Date 2014-01-27.02:16:33.088>
creator = 'terry.reedy'
dependencies = []
files = ['33758']
hgrepos = []
issue_num = 20401
keywords = ['patch']
message_count = 12.0
messages = ['209378', '209379', '209386', '209387', '209393', '209400', '209488', '209566', '209567', '292637', '292701', '292711']
nosy_count = 6.0
nosy_names = ['terry.reedy', 'ncoghlan', 'larry', 'python-dev', 'yselivanov', 'louielu']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'needs patch'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue20401'
versions = ['Python 3.3', 'Python 3.4']

[terryjreedy]

>>> 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.

[larryhastings]

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.

[terryjreedy]

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

[larryhastings]

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

[1st1]

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

[terryjreedy]

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

[1st1]

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

[python-dev]

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

[1st1]

Committed. Thank you, Terry.

[mlouielu]

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

[1st1]

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.

[terryjreedy]

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