Assertion failure in inspect.signature on unbound partialmethods

[anntzer]

BPO	33009
Nosy	@serhiy-storchaka, @1st1, @anntzer, @miss-islington
PRs	bpo-33009: Fix inspect.signature() for single-parameter partialmethods. #6004 [3.7] bpo-33009: Fix inspect.signature() for single-parameter partialmethods. (GH-6004) #6006 [3.6] bpo-33009: Fix inspect.signature() for single-parameter partialmethods. (GH-6004) #6007

^{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 = None
closed_at = <Date 2018-03-06.18:49:27.672>
created_at = <Date 2018-03-06.07:33:47.330>
labels = ['3.7', '3.8', 'type-bug', 'library']
title = 'Assertion failure in inspect.signature on unbound partialmethods'
updated_at = <Date 2018-03-06.18:49:27.671>
user = 'https://github.com/anntzer'

bugs.python.org fields:

activity = <Date 2018-03-06.18:49:27.671>
actor = 'yselivanov'
assignee = 'none'
closed = True
closed_date = <Date 2018-03-06.18:49:27.672>
closer = 'yselivanov'
components = ['Library (Lib)']
creation = <Date 2018-03-06.07:33:47.330>
creator = 'Antony.Lee'
dependencies = []
files = []
hgrepos = []
issue_num = 33009
keywords = ['patch']
message_count = 6.0
messages = ['313309', '313310', '313340', '313345', '313354', '313356']
nosy_count = 4.0
nosy_names = ['serhiy.storchaka', 'yselivanov', 'Antony.Lee', 'miss-islington']
pr_nums = ['6004', '6006', '6007']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue33009'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

[anntzer]

The following example crashes Python 3.6:

    from functools import partialmethod
    import inspect

    class T:
        g = partialmethod((lambda self, x: x), 1)

print(T().g())  # Correctly returns 1.
print(T.g(T()))  # Correctly returns 1.
print(inspect.signature(T.g))  # Crashes.

with

  File "/usr/lib/python3.6/inspect.py", line 3036, in signature
    return Signature.from_callable(obj, follow_wrapped=follow_wrapped)
  File "/usr/lib/python3.6/inspect.py", line 2786, in from_callable
    follow_wrapper_chains=follow_wrapped)
  File "/usr/lib/python3.6/inspect.py", line 2254, in _signature_from_callable
    assert first_wrapped_param is not sig_params[0]
IndexError: tuple index out of range

[serhiy-storchaka]

This is not a crash, but an assertion failure.

The assertion was added in bpo-30149.

[1st1]

Yeah, that assertion needs to be tweaked a little bit. Created a PR.

[1st1]

New changeset 8a38721 by Yury Selivanov in branch 'master':
bpo-33009: Fix inspect.signature() for single-parameter partialmethods. (GH-6004)
8a38721

[miss-islington]

New changeset 112f799 by Miss Islington (bot) in branch '3.7':
bpo-33009: Fix inspect.signature() for single-parameter partialmethods. (GH-6004)
112f799

[miss-islington]

New changeset 387a055 by Miss Islington (bot) in branch '3.6':
bpo-33009: Fix inspect.signature() for single-parameter partialmethods. (GH-6004)
387a055