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inspect.signature doesn't always return a signature #66000
Description
| BPO | 21801 |
|---|---|
| Nosy | @ncoghlan, @larryhastings, @PCManticore, @1st1 |
| Files |
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 2014-06-23.17:24:02.008>
created_at = <Date 2014-06-18.12:41:45.841>
labels = ['type-feature', 'library']
title = "inspect.signature doesn't always return a signature"
updated_at = <Date 2014-06-23.17:24:36.614>
user = 'https://github.com/PCManticore'bugs.python.org fields:
activity = <Date 2014-06-23.17:24:36.614>
actor = 'yselivanov'
assignee = 'yselivanov'
closed = True
closed_date = <Date 2014-06-23.17:24:02.008>
closer = 'python-dev'
components = ['Library (Lib)']
creation = <Date 2014-06-18.12:41:45.841>
creator = 'Claudiu.Popa'
dependencies = []
files = ['35682', '35710']
hgrepos = []
issue_num = 21801
keywords = ['patch', 'needs review']
message_count = 5.0
messages = ['220936', '221103', '221114', '221368', '221369']
nosy_count = 5.0
nosy_names = ['ncoghlan', 'larry', 'Claudiu.Popa', 'python-dev', 'yselivanov']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue21801'
versions = ['Python 3.4', 'Python 3.5']
Activity
PCManticore commentedon Jun 18, 2014
Hello. I noticed the following behaviour while working with xmlrpc proxy methods.
Now, according to the documentation, inspect.signature should return a signature or fail, but in this case it returns the actual object, which is misleading at least. This happens because _Method implements a proxy __getattr__, any accessed attribute becoming again a _Method. At the same time, inspect.signature happily uses
try:
obj.__signature__
except AttributeError:
...
to obtain the signature, if present.
The attached patch checks if __signature__ is an actual Signature object. I searched, but couldn't find any, if __signature__ can be anything, so I hope that this approach works.
1st1 commentedon Jun 20, 2014
This behaviour is indeed a bug. However, I think that the solution you propose is wrong.
If we ignore invalid contents of __signature__ we are masking a bug or incorrect behaviour. In this case, you should have checked the requested attribute name in '__getattr__', and return something other than _Method, if it is a '__signature__'.
Please find attached a patch, that checks if __signature__ is an instance of Signature class, and raises a TypeError if it isn't.
PCManticore commentedon Jun 20, 2014
Your patch looks good to me.
python-dev commentedon Jun 23, 2014
New changeset cc0f5d6ccb70 by Yury Selivanov in branch '3.4':
inspect: Validate that __signature__ is None or an instance of Signature.
http://hg.python.org/cpython/rev/cc0f5d6ccb70
New changeset fa5b985f0920 by Yury Selivanov in branch 'default':
inspect: Validate that __signature__ is None or an instance of Signature.
http://hg.python.org/cpython/rev/fa5b985f0920
1st1 commentedon Jun 23, 2014
Fixed in 3.4 and 3.5.
Thanks for the bug report!