inspect: getmembers calls properties

[jnsdrtlf]

BPO	38337
Nosy	@csabella, @hongweipeng, @jnsdrtlf
PRs	bpo-38337: Change getattr to inspect.getattr_static #16521

^{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 = None
created_at = <Date 2019-10-01.12:01:59.088>
labels = ['type-bug', 'library', '3.9']
title = 'inspect: getmembers calls properties'
updated_at = <Date 2020-03-29.19:22:40.724>
user = 'https://github.com/jnsdrtlf'

bugs.python.org fields:

activity = <Date 2020-03-29.19:22:40.724>
actor = 'jnsdrtlf'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-10-01.12:01:59.088>
creator = 'jnsdrtlf'
dependencies = []
files = []
hgrepos = []
issue_num = 38337
keywords = ['patch']
message_count = 9.0
messages = ['353688', '353698', '353871', '353872', '353895', '353900', '360715', '360748', '365274']
nosy_count = 3.0
nosy_names = ['cheryl.sabella', 'hongweipeng', 'jnsdrtlf']
pr_nums = ['16521']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38337'
versions = ['Python 3.9']

[jnsdrtlf]

When calling inspect.getmembers on a class that has a property (@Property), the property will be called by the getattr call in getmembers.

Example:

import inspect

class Example:
    def __init__(self, var):
        self._var = var
        print('__init__')

    def foo(self, bar):
        print(bar)
        print('foo')

    @property
    def var(self):
        print('Access property')
        return self._var


if __name__ == '__main__':
    ex = Example('Hello')
    print('--- getmembers from instance ---')
    print(inspect.getmembers(ex))
    print('--- getmembers from class    ---')
    print(inspect.getmembers(Example))

Result:

__init__
--- getmembers from instance ---
Access property
[('__class__', <attribute '__class__' of 'object' objects>), ..., ('var', 'Hello')]
--- getmembers from class ---
[('__class__', <attribute '__class__' of 'object' objects>), ..., ('var', <property object at 0x...>)]

Expected:

__init__
--- getmembers from instance ---
[('__class__', <attribute '__class__' of 'object' objects>), ..., ('var', <property object at 0x...>)]
--- getmembers from class ---
[('__class__', <attribute '__class__' of 'object' objects>), ..., ('var', <property object at 0x...>)]

[s-sanjay]

the issue happens in 2.7 as well

[hongweipeng]

The results of this example are different from mine(version 3.7.4).

__init__
--- getmembers from instance ---
Access property
[('__class__', <class '__main__.Example'>), ... ('var', 'Hello')]
--- getmembers from class    ---
[('__class__', <class 'type'>),'var', <property object at 0x>)]

[jnsdrtlf]

The results of this example are different from mine(version 3.7.4)

I do not really see any difference. What do you mean?

[hongweipeng]

I mean why member __class__ is expected to be <attribute '__class__'...>). I check PR16521,for class, it always gets <attribute '__class__'...>).

[jnsdrtlf]

Oh, yes I see what you mean. That's my fault, it seems like I copied the wrong line. Sorry.

But the important piece is the 'var' attribute. Sorry for the confusion.

[csabella]

Here is a link to the discussion of this on ideas:
https://discuss.python.org/t/implement-inspect-getmembers-static/2550

[jnsdrtlf]

Here is a link to the discussion of this on ideas

Thank you for posting the link.

I feel like I came to a dead end with this issue. As I am fairly new to CPython and have never contributed to this project before, I have no idea how to address this and to whom. Maybe this is just to irrelevant and not important, but even then we should probably close this issue or mark it as "indefinitely postponed" or something similar.

[jnsdrtlf]

I'm still thinking about this bug/issue/undefined behaviour. Today I wanted to test its behaviour with async:

import inspect


class Foo:
    def __init__(self, bar):
        self._bar = bar

@property
async def spam(self):
    print('Called spam')
    return self._bar

if __name__ == '__main__':
    instance = Foo('eggs')
    members = inspect.getmembers(instance)

This will result in a RuntimeWarning:

RuntimeWarning: coroutine 'Foo.spam' was never awaited
members = inspect.getmembers(instance)
RuntimeWarning: Enable tracemalloc to get the object allocation traceback

Sure, async properties might not be particularly beautiful or best-practice, but I frequently stumble upon code where getmembers would fail – just like this example. However, I am still clueless about what to do.