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- """Trait types for events."""
- from __future__ import annotations
- import logging
- import typing as t
- from traitlets import TraitError, TraitType
- baseclass = TraitType
- if t.TYPE_CHECKING:
- baseclass = TraitType[t.Any, t.Any] # type:ignore[misc]
- class Handlers(baseclass): # type:ignore[type-arg]
- """A trait that takes a list of logging handlers and converts
- it to a callable that returns that list (thus, making this
- trait pickleable).
- """
- info_text = "a list of logging handlers"
- def validate_elements(self, obj: t.Any, value: t.Any) -> None:
- """Validate the elements of an object."""
- if len(value) > 0:
- # Check that all elements are logging handlers.
- for el in value:
- if isinstance(el, logging.Handler) is False:
- self.element_error(obj)
- def element_error(self, obj: t.Any) -> None:
- """Raise an error for bad elements."""
- msg = f"Elements in the '{self.name}' trait of an {obj.__class__.__name__} instance must be Python `logging` handler instances."
- raise TraitError(msg)
- def validate(self, obj: t.Any, value: t.Any) -> t.Any:
- """Validate an object."""
- # If given a callable, call it and set the
- # value of this trait to the returned list.
- # Verify that the callable returns a list
- # of logging handler instances.
- if callable(value):
- out = value()
- self.validate_elements(obj, out)
- return out
- # If a list, check it's elements to verify
- # that each element is a logging handler instance.
- if isinstance(value, list):
- self.validate_elements(obj, value)
- return value
- self.error(obj, value)
- return None # type:ignore[unreachable]
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