How can mypy accept pydantic's constr() types?

I have this code:

from pydantic import BaseModel, constr

DeptNumber = constr(min_length=6, max_length=6)

class MyStuff(BaseModel):
    dept: DeptNumber

ms = MyStuff(dept = "123456")

deptnr.py:6: error: Variable "deptnr.DeptNumber" is not valid as a type
deptnr.py:6: note: See https://mypy.readthedocs.io/en/latest/common_issues.html#variables-vs-type-aliases

The provided link doesn't seem to really address my problem (I'm not using Type).

This happens with or without this mypy.ini:

[mypy]
plugins = pydantic.mypy

[pydantic-mypy]
init_typed = true

Initially I also had that error in a Pydantic choice as below, but I got around that by using Python's Literal instead.

DIR = choice(["North", "East", "South", "West"])

What do I need to change to make mypy happy with my Pydantic constr?

Solution

You can try to use Field from Pydantic :

from pydantic import BaseModel, Field

class MyStuff(BaseModel):
    dept: str = Field(..., min_length=6, max_length=6)

It seems working for me.