Full subclass support for nested schemas.

[Jerry-Ma]

Hi,

I have encounter some issues in integrating this package with the python's new dataclasses.dataclass. Most of them is due to the lack of customizability of the core classes including Schema, Optional, etc.

This pull request contains the following changes:

• Added **kwargs to the function signature of Schema.validate(). This allows subclass to override the behavior of validate in a propagate-able fashion. Nested schema.Schema class will ignore any kwargs, but nested MySchema class will behave accordingly. This fix A post validation hook at the schema level would be handy. #262 (@tolomea). Moreover, the kwargs passed to validate() is picked up by the Optional(default=) value when it is a callable:

assert Schema({Optional('a', default=lambda **k: k['some_value'])}).validate({}, some_value=1) == {'a': 1}

• Fix Derived class from Optional is not allowed #265 (@raoyitao), by changing the the hardcoded type check for Optional. This allows one to implement MyOptional that consumes the kwargs passed from validate to callable default more integrated:

class MyOptional(Optional):
    @property
    def default(self):
        def wrapped(**k):
            return k['some_value']
        return wrapped
    @default.setter
    def default(self, _):
        pass # this is needed to satisfy the Optional.__init__ which does `self.default=default`

• Added **kwargs to the signature of Schema.json_schema(), and changed the handling of default values such that callable will be evaluated with the kwargs. This makes it more inline with the behavior of the Schema.validate:

    def default_func(**kwargs):
        return 'Hello, ' + kwargs['name']
    s = Schema({Optional("test", default=default_func): str})
    assert s.json_schema("my-id", name='World!') == {
        "$schema": "http://json-schema.org/draft-07/schema#",
        "$id": "my-id",
        "properties": {"test": {"default": "Hello, World!", "type": "string"}},
        "required": [],
        "additionalProperties": False,
        "type": "object",
    }

For more details of the changes and their implications, please take a look at the test cases I added.

Please let me know what you think!

[skorokithakis]

This seems great, thank you! I especially appreciate the detailed PR description. Could you add some documentation to the README about these features so we can merge?

[Jerry-Ma]

@skorokithakis

Sorry for the long wait. I've just updated the README with a short example demonstrate this feature.

[skorokithakis]

Looks good, thanks!