inspect.getmembers does not retrive dataclass's __dataclass_fields__ properly

[corona10]

BPO	34122
Nosy	@ericvsmith, @serhiy-storchaka, @1st1, @corona10, @tirkarthi
Files	inspect_dataclass.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = <Date 2018-07-16.06:13:42.968>
created_at = <Date 2018-07-16.04:12:50.280>
labels = ['3.8', '3.7', 'library']
title = "inspect.getmembers does not retrive dataclass's __dataclass_fields__ properly"
updated_at = <Date 2018-07-16.06:13:42.966>
user = 'https://github.com/corona10'

bugs.python.org fields:

activity = <Date 2018-07-16.06:13:42.966>
actor = 'corona10'
assignee = 'none'
closed = True
closed_date = <Date 2018-07-16.06:13:42.968>
closer = 'corona10'
components = ['Library (Lib)']
creation = <Date 2018-07-16.04:12:50.280>
creator = 'corona10'
dependencies = []
files = ['47693']
hgrepos = []
issue_num = 34122
keywords = []
message_count = 3.0
messages = ['321706', '321707', '321711']
nosy_count = 5.0
nosy_names = ['eric.smith', 'serhiy.storchaka', 'yselivanov', 'corona10', 'xtreak']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue34122'
versions = ['Python 3.7', 'Python 3.8']

[corona10]

When I execute this script.

import inspect
from dataclasses import *
import enum

@dataclass
class SimpleDataObject(object):
    field_a: int = field()
    field_b: str = "asdad"

print([a[0] for a in inspect.getmembers(SimpleDataObject)])

I expected

['__annotations__', '__class__', '__dataclass_fields__', '__dataclass_params__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'field_a', 'field_b']

but got

['__annotations__', '__class__', '__dataclass_fields__', '__dataclass_params__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'field_b']

If this behavior is not intended, I propose a new patch with providing Inspect.isdataclass for Python 3.8 and Inspect._is_dataclss for Python 3.7

corona10@c266517

[tirkarthi]

I think there is some note about this on the doc as below :

https://docs.python.org/3/library/dataclasses.html#dataclasses.field . Relevant commit : 98d50cb

If the default value of a field is specified by a call to field(), then the class attribute for this field will be replaced by the specified default value. If no default is provided, then the class attribute will be deleted. The intent is that after the dataclass() decorator runs, the class attributes will all contain the default values for the fields, just as if the default value itself were specified.

Using a default value returns the parameter in the inspect module as below :

➜ cpython git:(master) ✗ cat foo.py
import inspect
from dataclasses import *
import enum

@dataclass
class SimpleDataObject(object):
    field_a: int = field(default=10)
    field_b: str = "asdad"

print([a[0] for a in inspect.getmembers(SimpleDataObject)])
➜ cpython git:(master) ✗ ./python foo.py
['__annotations__', '__class__', '__dataclass_fields__', '__dataclass_params__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'field_a', 'field_b']

I think this is an intended behavior as above and a test case could be added or docs could be improved about this with the inspect example?

Thanks

[corona10]

@XTreak
Yeah... It looks like intended.
Closing this issue!