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Showing content from https://github.com/pydantic/pydantic/issues/635 below:

The validator of the type hints classes are evaluated with apparently weird input · Issue #635 · pydantic/pydantic · GitHub

Bug or Question

• OS: Debian
• Python version import sys; print(sys.version): 3.7.2
• Pydantic version import pydantic; print(pydantic.VERSION): 0.29

Hi,

I work with some models and below I tried to simplify the idea:

class Parent(BaseModel):
    siblings: List[Parent]

    @validator('siblings', whole=True, pre=True)
    def validate_siblings(cls, siblings):
        ...

class Child1(Parent):
    siblings: List[Union[Child2, Child3]]

class Child2(Parent):
    siblings: List[Union[Child3, Child5, Child6]]

.....

Note that the parent validator may be overwritten or not, it doesn't matter in this situation.

When a Child2 is instantiated (with siblings=[child6_obj] for example) --> the validator is called for the Child2 class. The problem is that all the validators for the possible Child2.siblings types are also evaluated (which are Child3, Child5, Child6). And from my debugging, they are called with child_obj.dict(), so validate_siblings validator receives a list of dicts as param even if the Child2 object is instantiated with a list of objects (siblings=[child6_obj]).

In my case, the validator of Child3 will raise an error.

First of all, Is this the correct behavior?

Secondly, do you spot any bad practice/idea in my snippet?

--- EDIT

Some more details about def validate_siblings(cls, siblings) implementation:

• the main purpose of the method is to check the types of items inside siblings param (which is a list)
• so, for example, when Child1 is instantiated (c = Child1(siblings=[obj1, obj2])), I expect the validator is called with [obj1, obj2], and its logic is to check if both objects in the list are instances of Child2 or Child3. I achieve this by looking in Child1.__annotations__.
• to reiterate, I don't expect a dict in validate_siblings validator, but only the objects I use in my code. Maybe I didn't understand how validators work and what are the situations in which they are called/evaluated.

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