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BaseModel.construct does not set aliased fields consistently with standard instantiation #4192

3 tasks done
kylebamos opened this issue Jun 28, 2022 · 0 comments · Fixed by #4191
3 tasks done
bug V1 Bug related to Pydantic V1.X


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  • I added a descriptive title to this issue
  • I have searched (google, github) for similar issues and couldn't find anything
  • I have read and followed the docs and still think this is a bug


Output of python -c "import pydantic.utils; print(pydantic.utils.version_info())":

             pydantic version: 1.8.2
            pydantic compiled: False
                 install path: /Users/kyleamos/Library/Caches/pypoetry/virtualenvs/api-KwVDv1SR-py3.9/lib/python3.9/site-packages/pydantic
               python version: 3.9.1 (default, Jan 18 2022, 12:54:24)  [Clang 13.0.0 (clang-1300.0.29.30)]
                     platform: macOS-12.1-arm64-arm-64bit
     optional deps. installed: ['email-validator', 'typing-extensions']
from pydantic import BaseConfig, BaseModel, Field

class Foo(BaseModel):
    class Config(BaseConfig):
        allow_population_by_field_name = True

    bar_: int = Field(..., alias="bar")

expected_value = 2
assert Foo(bar=expected_value).bar_ == expected_value
assert Foo.construct(bar=expected_value).bar_ == expected_value  # AttributeError: 'Foo' object has no attribute 'bar_' 
@kylebamos kylebamos added the bug V1 Bug related to Pydantic V1.X label Jun 28, 2022
samuelcolvin pushed a commit that referenced this issue Aug 11, 2022
* Fix a bug where BaseModel.construct would not appropriately respect field aliases

* Perhaps do not raise on construct and just apply the fix

* Fix quotes and remove check on allow_population_by_field_name

* Fix lint

* Fix lint, remove bad arg

* Black formatted

* Mmmm black formatter and single quotes linting, what a world

* Added change file

* PR feedback

Co-authored-by: Kyle Amos <>
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bug V1 Bug related to Pydantic V1.X
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