Modify field value according to a sub-models field?

[dmach]

Hi,
I want to use pydantic to store main settings and per-host settings.
The host settings should inherit their default values from the main settings.
If I manipulate the main settings, the changes should automatically propagate to the host settings as long as the fields are not explicitly set to anything but None.

I was trying to use validators, but they seem to set the value and when I change the nested main config, the change doesn't get propagated.

Isn't there something that would allow me modifying the returned value from a field while keeping the stored value intact?
Any ideas?

Example code:

from pydantic import *
from typing import *

class MainConfig(BaseModel):
    verbose: bool = Field(default=False)

class HostConfig(BaseModel):
    model_config = ConfigDict(
        extra="forbid",
        validate_assignment=True,
        validate_default=True,
        validate_return=True,
    )

    main_config: MainConfig = Field()
    hostname: str = Field()
    verbose: Optional[bool] = Field(default=None)

main = MainConfig()
assert main.verbose == False

host = HostConfig(main_config=main, hostname="example.com", verbose=None)
assert host.verbose == False
# ^^^ if host.verbose is None, I want to return main_config.verbose instead

# when main.verbose changes, host.verbose follows
main.verbose = True
assert host.verbose == True

# when host.verbose != None, return the explicitly set value
host.verbose = False
main.verbose = True
assert host.verbose == False

# when host.verbose == None, return the inherited value again
host.verbose = None
main.verbose = True
assert host.verbose == True