Compatibility layer for pydantic v1/v2
Pydantic 2 was a major release that completely changed the pydantic API.
For applications, this is not a big deal, as they can pin to whatever version of pydantic they need. But for libraries that want to exist in a broader environment, pinning to a specific version of pydantic is not always an option (as it limits the ability to co-exist with other libraries).
This package provides (unofficial) compatibility mixins and function adaptors for pydantic v1-v2 cross compatibility. It allows you to use either v1 or v2 API names, regardless of the pydantic version installed. (Prefer using v2 names when possible).
Tests are run on Pydantic v1.8 and up
The API conversion is not exhaustive, but suffices for many of the use cases I have come across. It is in use by the following libraries:
Feel free to open an issue or PR if you find it useful, but lacking features you need.
Not much! :joy:
Mostly it serves to translate names from one API to another. It backports the v2 API to v1 (so you can v2 names in a pydantic1 runtime), and forwards the v1 API to v2 (so you can use v1 names in a v2 runtime without deprecation warnings).
While pydantic2 does offer deprecated access to the v1 API, if you explicitly wish to support pydantic1 without your users seeing deprecation warnings, then you need to do a lot of name adaptation depending on the runtime pydantic version. This package does that for you.
It does not do any significantly complex translation of API logic. For custom types, you will still likely need to add class methods to support both versions of pydantic.
It also does not prevent you from needing to know a what's changing under the hood in pydantic 2. You should be running tests on both versions of pydantic to ensure your library works as expected. This library just makes it much easier to support both versions in a single codebase without a lot of ugly conditionals and boilerplate.
from pydantic import BaseModel
from pydantic_compat import PydanticCompatMixin
from pydantic_compat import field_validator # or 'validator'
from pydantic_compat import model_validator # or 'root_validator'
class MyModel(PydanticCompatMixin, BaseModel):
x: int
y: int = 2
# prefer v2 dict, but v1 class Config is supported
model_config = {'frozen': True}
@field_validator('x', mode='after')
def _check_x(cls, v):
if v != 42:
raise ValueError("That's not the answer!")
return v
@model_validator('x', mode='after')
def _check_x(cls, v: MyModel):
# ...
return v
You can now use the following attributes and methods regardless of the pydantic version installed (without deprecation warnings):
v1 name | v2 name |
---|---|
obj.dict() |
obj.model_dump() |
obj.json() |
obj.model_dump_json() |
obj.copy() |
obj.model_copy() |
Model.construct |
Model.model_construct |
Model.schema |
Model.model_json_schema |
Model.validate |
Model.model_validate |
Model.parse_obj |
Model.model_validate |
Model.parse_raw |
Model.model_validate_json |
Model.update_forward_refs |
Model.model_rebuild |
Model.__fields__ |
Model.model_fields |
Model.__fields_set__ |
Model.model_fields_set |
Field
notespydantic_compat.Field
will remove outdated fields (const
) and translate
fields with new names:
v1 name | v2 name |
---|---|
min_items |
min_length |
max_items |
max_length |
regex |
pattern |
allow_mutation |
not frozen |
metadata |
json_schema_extra |
var = Field(..., const='val')
, use var: Literal['val'] = 'val'
it works in both v1 and v2unique_items
and v2's Set[]
semantics. See https://github.com/pydantic/pydantic-core/issues/296 for
discussion.pydantic_compat.field_validator
then the
signature must match the pydantic (v2) field_validator
signature (regardless)
of the pydantic version installed. Similarly, if you choose to use
pydantic_compat.validator
then the signature must match the pydantic
(v1) validator
signature.BaseModel.__fields__
in v1 is a dict of {'field_name' -> ModelField}
whereas in v2 BaseModel.model_fields
is a dict of {'field_name' -> FieldInfo}
. FieldInfo
is a much simpler object that ModelField, so it is
difficult to directly support complicated v1 usage of __fields__
.
pydantic-compat
simply provides a name addaptor that lets you access many of
the attributes you may have accessed on ModelField
in v1 while operating in
a v2 world, but ModelField
methods will not be made available. You'll need
to update your usage accordingly.
in V2, pydantic.model_validator(..., mode='after')
passes a model instance
to the validator function, whereas pydantic.v1.root_validator(..., pre=False)
passes a dict of {'field_name' -> validated_value}
to the
validator function. In pydantic-compat, both decorators follow the semantics
of their corresponding pydantic versions, but root_validator
gains
parameter construct_object: bool=False
that matches the model_validator
behavior (only when mode=='after'
). If you want that behavior though, prefer
using model_validator
directly.