Usage with mypy

Pydantic works with mypy provided you use the "annotation only" version of required fields:

from datetime import datetime
from typing import List, Optional
from pydantic import BaseModel, NoneStr

class Model(BaseModel):
    age: int
    first_name = 'John'
    last_name: NoneStr = None
    signup_ts: Optional[datetime] = None
    list_of_ints: List[int]

m = Model(age=42, list_of_ints=[1, '2', b'3'])
# > 42

# will raise a validation error for age and list_of_ints

(This script is complete, it should run "as is")

You can also run it through mypy with:

mypy \
  --ignore-missing-imports \
  --follow-imports=skip \
  --strict-optional \

Strict Optional🔗

For your code to pass with --strict-optional you need to to use Optional[] or an alias of Optional[] for all fields with None default, this is standard with mypy.

Pydantic provides a few useful optional or union types:

  • NoneStr aka. Optional[str]
  • NoneBytes aka. Optional[bytes]
  • StrBytes aka. Union[str, bytes]
  • NoneStrBytes aka. Optional[StrBytes]

If these aren't sufficient you can of course define your own.