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classification
Title: __class__ not set defining 'X' as
Type: Stage:
Components: Interpreter Core Versions: Python 3.8
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: cdce8p, conqp, xtreak, zzzeek
Priority: normal Keywords:

Created on 2020-08-24 23:32 by zzzeek, last changed 2022-04-11 14:59 by admin.

Messages (4)
msg375863 - (view) Author: mike bayer (zzzeek) * Date: 2020-08-24 23:32
This is likely related or a dupe of https://bugs.python.org/issue29270, but the error message is different.  I'm posting this to confirm it's the same issue, or not, and to at least provide a google result for people who also see this error as 29270 seems to imply this might not be fixable.

Like 29270, it involves the fact that the interpreter seems to be looking at my super() call inside of a method without actually calling it, and then getting upset about __classcell__:



from typing import NamedTuple


class X(NamedTuple):
    a: str
    b: str

    # comment this out to remove the issue
    def foo(self):
        return super(X, self)


and that's it!  on my interpreter:

Python 3.8.3 (default, May 23 2020, 16:34:37) 
[GCC 9.3.1 20200408 (Red Hat 9.3.1-2)] on linux

I get:

$ python test3.py 
Traceback (most recent call last):
  File "test3.py", line 4, in <module>
    class X(NamedTuple):
RuntimeError: __class__ not set defining 'X' as <class '__main__.X'>. Was __classcell__ propagated to type.__new__?

The most surprising thing is that this seems extremely basic and google is not finding this error message for me.
msg375879 - (view) Author: Karthikeyan Singaravelan (xtreak) * (Python committer) Date: 2020-08-25 09:53
The example used to raise deprecation warning in python 3.7

python3.7 -Wall ../backups/bpo41629.py
../backups/bpo41629.py:4: DeprecationWarning: __class__ not set defining 'X' as <class '__main__.X'>. Was __classcell__ propagated to type.__new__?
  class X(NamedTuple):

It was converted into RuntimeError in https://github.com/python/cpython/commit/f5e7b1999f46e592d42dfab51563ea5411946fb7 . Related https://bugs.python.org/issue23722
msg375880 - (view) Author: Karthikeyan Singaravelan (xtreak) * (Python committer) Date: 2020-08-25 10:05
Related SO questions : 

* https://stackoverflow.com/questions/61543768/super-in-a-typing-namedtuple-subclass-fails-in-python-3-8
* https://stackoverflow.com/questions/41343263/provide-classcell-example-for-python-3-6-metaclass
msg384490 - (view) Author: Richard Neumann (conqp) * Date: 2021-01-06 11:25
I just stumbled across this issue trying to resolve this: https://bugs.python.org/issue42765?

While this fails:

from typing import NamedTuple


class Spamm(NamedTuple):

    foo: int
    bar: str

    def __getitem__(self, index_or_key):
        """Returns the respective item."""
        if isinstance(index_or_key, str):
            try:
                return getattr(self, index_or_key)
            except AttributeError:
                raise IndexError(index_or_key) from None

        return super().__getitem__(index_or_key)

    def keys(self):
        return self._fields


def main():

    spamm = Spamm(12, 'hello')
    print(dir(spamm))
    print(spamm._fields)
    d = dict(spamm)
    print(d)


if __name__ == '__main__':
    main()


with

Traceback (most recent call last):
  File "/home/neumann/test.py", line 4, in <module>
    class Spamm(NamedTuple):
RuntimeError: __class__ not set defining 'Spamm' as <class '__main__.Spamm'>. Was __classcell__ propagated to type.__new__?


The following works:

from typing import NamedTuple


def _getitem(instance, index_or_key):
    """Returns the respective item."""

    if isinstance(index_or_key, str):
        try:
            return getattr(instance, index_or_key)
        except AttributeError:
            raise IndexError(index_or_key) from None

    return super().__getitem__(index_or_key)


def dicttuple(cls: tuple):
    """Extends a tuple class with methods for the dict constructor."""

    cls.keys = lambda self: self._fields
    cls.__getitem__ = _getitem
    return cls


@dicttuple
class Spamm(NamedTuple):

    foo: int
    bar: str


def main():

    spamm = Spamm(12, 'hello')
    print(dir(spamm))
    print(spamm._fields)
    d = dict(spamm)
    print(d)


if __name__ == '__main__':
    main()


And produces:

['__add__', '__annotations__', '__class__', '__class_getitem__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__module__', '__mul__', '__ne__', '__new__', '__orig_bases__', '__reduce__', '__reduce_ex__', '__repr__', '__rmul__', '__setattr__', '__sizeof__', '__slots__', '__str__', '__subclasshook__', '_asdict', '_field_defaults', '_fields', '_make', '_replace', 'bar', 'count', 'foo', 'index', 'keys']
('foo', 'bar')
{'foo': 12, 'bar': 'hello'}


I am a bit baffled, why it works when the method is injected via a decorator.
History
Date User Action Args
2022-04-11 14:59:35adminsetgithub: 85795
2021-09-23 12:36:30cdce8psetnosy: + cdce8p
2021-01-06 11:25:59conqpsetnosy: + conqp
messages: + msg384490
2020-08-29 22:26:31terry.reedysettitle: __class__ not set defining 'X' as <class '__main__.X'>. Was __classcell__ propagated to type.__new__? -> __class__ not set defining 'X' as <class '__main__.X'>
2020-08-25 10:05:58xtreaksetmessages: + msg375880
2020-08-25 09:53:36xtreaksetnosy: + xtreak
messages: + msg375879
2020-08-24 23:32:59zzzeekcreate