each_item is applied recursively

[gsakkis]

Setting each_item=True to a validator of a nested collection is apparently called recursively for each singleton of the collection, instead of the items of the collection:

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

pydantic version: 1.4
pydantic compiled: True
python version: 3.7.1 (default, Dec 14 2018, 19:46:24)  [GCC 7.3.0]
platform: Linux-4.4.0-173-generic-i686-with-debian-stretch-sid
optional deps. installed: ['typing-extensions']

from pydantic import validator
from pydantic.dataclasses import dataclass
from typing import Sequence

@dataclass
class DemoModel:
    square_numbers: Sequence[int] = ()
    square_number_lists: Sequence[Sequence[int]] = ()

    @validator('square_numbers', each_item=True)
    def check_squares(cls, v):
        assert v ** 0.5 % 1 == 0, f'{v} is not a square number'
        return v

    @validator('square_number_lists', each_item=True)
    def check_square_lists(cls, v):
        assert isinstance(v, Sequence), type(v)
        return v

print(DemoModel(square_numbers=[1, 4, 9]))
print(DemoModel(square_number_lists=[[1, 4, 9], [16, 25]]))

DemoModel(square_numbers=[1, 4, 9], square_number_lists=())
Traceback (most recent call last):
  File "foo.py", line 22, in <module>
    print(DemoModel(square_number_lists=[[1, 4, 9], [16, 25]]))
  File "<string>", line 4, in __init__
  File "pydantic/dataclasses.py", line 83, in pydantic.dataclasses._process_class._pydantic_post_init
    # Raise because not adding these methods would break the "frozen-ness"
pydantic.error_wrappers.ValidationError: 5 validation errors for DemoModel
square_number_lists -> 0 -> 0
  <class 'int'> (type=assertion_error)
square_number_lists -> 0 -> 1
  <class 'int'> (type=assertion_error)
square_number_lists -> 0 -> 2
  <class 'int'> (type=assertion_error)
square_number_lists -> 1 -> 0
  <class 'int'> (type=assertion_error)
square_number_lists -> 1 -> 1
  <class 'int'> (type=assertion_error)

[samuelcolvin]

humm, I guess I think this would be very hard to change and might be wanted, you'd be best to skip each_item=True and do the validation on the whole object.

If that doesn't work for you, what would you propose?

[gsakkis]

At the very least the documentation should mention the current behavior, it's surely not expected. If backwards compatibility can be broken here, my suggestion would be to make each_item flat and add a new parameter, say flatten, with the current recursive behavior.