richdataclasses.md

With dataclasses Rich will essentially replace the dataclass __repr__ by inspecting the dataclass fields. It does this so it can know how to expand the dataclass on to multiple lines with indentation.

For example, here is a dataclass

@dataclass
class DC:
    foo: str
    bar: int

Rich can inspect the fields and generate this:

DC(
    foo="hello",
    bar=5
)

However Rich will respect a custom rerpr. For example:

@dataclass
class DC:
    foo: str
    bar: int
    
    def __repr__(self):
        return "DC is better than Marvel"

In the above case, Rich will call repr(dc) rather than inspecting the fields.

So Rich needs to know if that custom __repr__ is present.

The problem is that the cases with or without the custom __repr__, the dataclass instances both contain a __repr__. And Rich needs to know if it is the default one generated by the @dataclass decorator OR one provided by the user.

Since there is no dataclass base class, I can't just compare it to the baseclasses (via __mro__). In both cases the mro is (DC, object).

Before Python3.10 the __qualname__ attribute was different in dataclass generated reprs, and I could use that. Now in Python3.10 the __qualname__ attribute is identical in both cases.

Have you looked at the standard library implementation for pprint, specifically https://bugs.python.org/issue43080 and https://github.com/python/cpython/pull/24389/files ? That also checks for a custom repr, etc. Other than using "object" as a parameter name 😠, they use dataclasses.is_dataclass(item) to see if something is a dataclass, then they check if __wrapped__ is an attribute of the __repr__, followed by a check for "__create_fn__" in item.__repr__.__wrapped__.__qualname__.

Is the reprlib module of any help? Or hindrance?