Thomas <[email protected]> added the comment:
Scratch that last one, it leads to problem when mixing descriptors with actual
default values:
@dataclass
class Foo:
bar = field(default=some_descriptor)
# technically this is a descriptor field without a default value or at the
very least, the dataclass constructor can't know because it doesn't know what
field, if any, this delegates to. This means this will show up as optional in
the __init__ signature but it might not be.
bar = field(default=some_descriptor, default_factory=lambda:4)
# this could be a solve for the above problem. The dc constructor would
install the constructor at the class level and assign 4 to the instance
attribute in the __init__. Still doesn't tell the dc constructor if a field is
optional or not when it's default value is a descriptor and no default_factory
is passed. And it feels a lot more like hack than anything else.
So ignore my previous message. I'm still 100% behind the "descriptor" arg in
the field constructor, though :)
PS: Sorry for the noise, I just stumbled onto this problem for the nth-times
and I can't get my brain to shut off.
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<https://bugs.python.org/issue39247>
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