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Issue with ClassVar #276
Description
Hi there,
So I encountered the following issue. I have a base class with some ClassVars:
class MsgSpecSignatureModel(Struct):
dependency_name_set: ClassVar[Set[str]]
field_plugin_mappings: ClassVar[Dict[str, PluginMapping]]
return_annotation: ClassVar[Any]
signature_fields: Dict[str, SignatureField]
# ...I get the following error:
self = <msgspec.inspect._Translator object at 0x115541ad0>
def run(self):
# First construct a decoder to validate the types are valid
if self.protocol in (None, "msgpack"):
from ._core import MsgpackDecoder as Decoder
elif self.protocol == "json":
from ._core import JSONDecoder as Decoder
else:
raise ValueError("protocol must be one of None, 'msgpack', 'json'")
> Decoder(Tuple[self.types])
E TypeError: Type 'typing.ClassVar[typing.Set[str]]' is not supported
Activity
jcrist commentedon Jan 28, 2023
Thanks for opening this issue!
Due to type annotation limitations,
ClassVaris surprisingly non-trivial to support in the presence of PEP 563 (especially doing so efficiently).Previously I had punted on this and not supported it - to use ClassVars on structs with previous releases of msgspec you can use a
# type:comment instead of a true type annotation:This worked, but wasn't the most developer friendly.
After some thought (and reading CPython source code) I've successfully found a way to support
ClassVaron struct types for common cases. The fix is in #281.This won't successfully detect all
ClassVaruses whenPEP 563is enabled, but the cases that won't be detected are uncommon (and the limitations are documented). See the docs update in the PR for the limitations.I hope to cut a release early this week, so you should have access to this fix in the near-ish future.
In the future, please include the full traceback when reporting error messages, and at least the python line that caused the error. I was able to debug your issue because I was aware of the limitation you ran into, but if I wasn't I wouldn't be able to reproduce the error with only the code you posted.
Stackoverflow has a pretty good guide on what makes for a good bug report. Thanks!