5804 Simplify the configparser usage to get parsed attributes easily

[Shadow-Devil]

part of #5804.

Description

This adds a simple attribute access for ConfigParser so

from monai.bundle import ConfigParser
parser = ConfigParser({"a":"b"})
a = parser.get_parsed_content("a")

can be rewritten to

from monai.bundle import ConfigParser
parser = ConfigParser({"a":"b"})
a = parser.a

This only works for variables/methods that are not included in ConfigParser so e.g. parser.config would still get the whole config.
This PR only supports shallow attribute accesses, since the returned value will be a dict where you need to use ["key"] to get the content.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• New tests added to cover the changes.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.

[wyli]

Thanks, it looks good to me.

[Shadow-Devil]

One Idea was to change the get_config of ConfigItem like this:

class ConfigItem:
...
    def get_config(self) -> Any:
        """
        Get the config content of current config item.
        If the content is a dict it will wrap it with `DictWrapper` to allow attribute like access.

        """
        
        return self.config if not isinstance(self.config, dict) else DictWrapper(self.config)

class DictWrapper(UserDict):
    """
    Wrapper class to support attribute-style access to the dict items.
    """

    def __getattr__(self, key: str) -> Any:
        if key in self.data:
            item = self.data[key]
            return item if not isinstance(item, dict) else DictWrapper(item)
        raise AttributeError(f"'{self.__class__.__name__}' object has no attribute '{key}'")

This implementation wraps each dict into this DictWrapper which will in itself wrap each dict again into a DictWrapper.

[Shadow-Devil]

The problem with this implementation is, that nested content is not parsed/instantiated...

[wyli]

I'll merge this PR for now... for the nested cases, perhaps we'll introduce a new class for ConfigParser.config? do you plan to continue working on this @Shadow-Devil? otherwise @Nic-Ma and I can take over and enhance. we are fine with either way.

[Shadow-Devil]

Thanks @wyli, I think it would be better if you continue since I'm not sure how this new class should look like and there are some design decisions to make, which should be in line with the rest of the project. If you have a general plan on how this should look like, I'm happy to implement it :)

[wyli]

/build

[wyli]

/build