Patch unset attributes with MISSING during model serialization with exclude_unset#12905
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Patch unset attributes with MISSING during model serialization with exclude_unset#12905
MISSING during model serialization with exclude_unset#12905Conversation
… `exclude_unset`
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Viicos
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MISSING during model serialization with exclude_unsetMISSING during model serialization with exclude_unset
Member
It looks like the following behaves as expected? from typing import Annotated
from pydantic import BaseModel, WrapSerializer, model_serializer
def ser(v, h):
# not called
return h(v)
class Model(BaseModel):
a: Annotated[int, WrapSerializer(ser)] = 1
@model_serializer(mode='wrap')
def ser_model(self, handler):
rv = handler(self)
print(rv) # {}
return rv
m = Model()
m.model_dump(exclude_unset=True) |
Viicos
reviewed
Mar 18, 2026
Co-authored-by: Victorien <[email protected]>
Viicos
approved these changes
Mar 18, 2026
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Change Summary
This is a possible fix for #12888 that avoids regressing the tests previously added.
The approach is to use the missing sentinel to signal which fields are unset during serialization instead of removing them from the dictionary.
Note: I think this is probably user-observable with custom serializer functions (e.g. wrap serializers); I'm unsure if that means that this approach is not ok (or has to be limited only to when there are no model serializers present). We should discuss.
Related issue number
Fixes #12888
Checklist