Class Config

traitlets/config/loader.py:224–376

An attribute-based dict that can do smart merges. Accessing a field on a config object for the first time populates the key with either a nested Config object for keys starting with capitals or :class:`.LazyConfigValue` for lowercase keys, allowing quick assignments such as::

class Config(dict):  # type:ignore[type-arg]
    """An attribute-based dict that can do smart merges.

    Accessing a field on a config object for the first time populates the key
    with either a nested Config object for keys starting with capitals
    or :class:`.LazyConfigValue` for lowercase keys,
    allowing quick assignments such as::

        c = Config()
        c.Class.int_trait = 5
        c.Class.list_trait.append("x")

    """

    def __init__(self, *args: t.Any, **kwds: t.Any) -> None:
        dict.__init__(self, *args, **kwds)
        self._ensure_subconfig()

    def _ensure_subconfig(self) -> None:
        """ensure that sub-dicts that should be Config objects are

        casts dicts that are under section keys to Config objects,
        which is necessary for constructing Config objects from dict literals.
        """
        for key in self:
            obj = self[key]
            if _is_section_key(key) and isinstance(obj, dict) and not isinstance(obj, Config):
                setattr(self, key, Config(obj))

    def _merge(self, other: t.Any) -> None:
        """deprecated alias, use Config.merge()"""
        self.merge(other)

    def merge(self, other: t.Any) -> None:
        """merge another config object into this one"""
        to_update = {}
        for k, v in other.items():
            if k not in self:
                to_update[k] = v
            else:  # I have this key
                if isinstance(v, Config) and isinstance(self[k], Config):
                    # Recursively merge common sub Configs
                    self[k].merge(v)
                elif isinstance(v, LazyConfigValue):
                    self[k] = v.merge_into(self[k])
                else:
                    # Plain updates for non-Configs
                    to_update[k] = v

        self.update(to_update)

    def collisions(self, other: Config) -> dict[str, t.Any]:
        """Check for collisions between two config objects.

        Returns a dict of the form {"Class": {"trait": "collision message"}}`,
        indicating which values have been ignored.

        An empty dict indicates no collisions.