Assigning Pydantic Fields not by alias 2

Question

Why doesn't this work for my case?

# Windows 10
# Python 3.11.8
# Pydantic 2.7.3
# Mypy 1.10.0
"""mypy.ini
[mypy]
plugins = pydantic.mypy
"""
# https://stackoverflow.com/questions/69433904/assigning-pydantic-fields-not-by-alias
from pydantic import BaseModel, Field, ConfigDict


class Params(BaseModel):
    var_name: int = Field(alias='var_alias')

    model_config = ConfigDict(
        populate_by_name=True,
    )

Params(var_alias=5)  # no works
Params(var_name=5)   # works
"""
mypy .\tess.py
tess.py:20: error: Missing named argument "var_name" for "Params"  [call-arg]
Found 1 error in 1 file (checked 1 source file)
"""

My code is identical to Assigning Pydantic Fields not by alias but I get an error, I don't understand why
Expected:

mypy .\tess.py
Success: no issues found in 1 source file

Why doesn't it work for me? And gitlab-ci is also for me @toyotaSupra — Максим Федотов
– Максим Федотов, Commented Jun 6, 2024 at 11:33

Rafael Marques · Accepted Answer · 2024-06-07 12:13:37Z

1

Seems like you need to add a default value to work:

[mypy]
plugins = pydantic.mypy

from pydantic import BaseModel, Field, ConfigDict


class Params(BaseModel):
    var_name: int = Field(42, alias='var_alias')

    model_config = ConfigDict(
        populate_by_name=True,
    )

Params(var_alias=5)  # now works too
Params(var_name=5)   # works

Success: no issues found in 1 source file

answered Jun 7, 2024 at 12:13

Rafael Marques

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2 Comments

Максим Федотов Over a year ago

Is it possible without the default value?

Rafael Marques Over a year ago

I couldn't find anything without

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