Create Python Data Models with conditions

Question

How do I create pydantic model with conditions?

I have a pydantic model. It works well when declaring new class with this model as base. The problem I have is, the

• BaseUser.username should have
  • maxlength of 32 chars
  • minlength of 6 chars.
• BaseUser.password to be fixed to 64 chars. Not less, not more.

Is that any way that I can achieve it through datatypes?

> I know that I can do it with simple "if" statements, but I want it to be a datatype in pydantic model.

from pydantic import BaseModel

class BaseUser(BaseModel):
    id: int
    username: str
    password: str

Thank you.

Answer 1

Have you considered using Contraint types?

from pydantic import BaseModel, constr

class BaseUser(BaseModel):
    id: int
    username: constr(min_length=6, max_length=32)
    password: constr(min_length=64, max_length=64)

Sample output

>>> user = BaseUser(id='1', username='foo', password='4m*PbpA!*A2XUdvU@u0WTvvFRyNSMcndVm6@NkZwJR1afBb@G1i5*1vvh9z*g8xw'

ValidationError: 1 validation error for BaseUser
username
  ensure this value has at least 6 characters (type=value_error.any_str.min_length; limit_value=6)


>> user = BaseUser(id='1', username='foobar', password='4m*PbpA!*A2XU')

ValidationError: 1 validation error for BaseUser
password
  ensure this value has at least 64 characters (type=value_error.any_str.min_length; limit_value=64)

>>> user = BaseUser(id='1', username='foobar', password='4m*PbpA!*A2XUdvU@u0WTvvFRyNSMcndVm6@NkZwJR1afBb@G1i5*1vvh9z*g8xw')

>>> user.dict()
>>> 
{'id': 1,
 'username': 'foobar',
 'password': '4m*PbpA!*A2XUdvU@u0WTvvFRyNSMcndVm6@NkZwJR1afBb@G1i5*1vvh9z*g8xw'}

Just a heads-up: I have never used Pydantic before. So, there could be a better way to solve this.