copy_on_model_validation doesn't work for validate_arguments config

[assaf-orca]

Bug

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

pydantic version: 1.8.2
pydantic compiled: True
install path: /usr/local/lib/python3.8/site-packages/pydantic
python version: 3.8.12 (default, Sep  3 2021, 02:24:44)  [GCC 10.2.1 20210110]
platform: Linux-5.10.25-linuxkit-x86_64-with-glibc2.2.5
optional deps. installed: ['typing-extensions']

from typing import Set

from pydantic import validate_arguments


my_set = {"assaf"}
print(f"{id(my_set)=}")

def a(b: Set[str]):
    print(f"first {id(b)=}")


a(my_set)


@validate_arguments
def a(b: Set[str]):
    print(f"second {id(b)=}")


a(my_set)


@validate_arguments(config=dict(copy_on_model_validation=False))
def a(b: Set[str]):
    print(f"third {id(b)=}")


a(my_set)

""" 
... ... Model Config

copy_on_model_validation
whether or not inherited models used as fields should be reconstructed (copied) on validation instead of being kept untouched (default: True)
"""

output:

id(my_set)=139856697296704
first id(b)=139856697296704
second id(b)=139856688179456
third id(b)=139856688107584

I think with the decorator validate_arguments it's need to be same as the original python behavior, but if it doesn't the config should support it.

[hb2638]

This bug is still present in 1.10.5. Thx for reporting!!

[hramezani]

@assaf-orca When we validate a set, we always re-create it - same as we do with pydantic models, so the id changes
it's really a fundamental limitation/feature of Pydantic

[hb2638]

Why was this bug closed?
The bug is still present in the code.

"When we validate a set, we always re-create it" contradicts copy_on_model_validation being set to 'none'.

The code/validator should fault at when it's unable to honor the copy_on_model_validation of 'none'. (E.x.: It's given an iterator - or - you would need to convert the items in the sequence to make the contract work) instead of silently breaking the contract/requirement.

Without that type of enforcement, you'll just have people shooting themselves in the foot left and right because changes to the collection or object are not being propagated to the caller.