@@ -85,7 +85,9 @@ class BaseLearner(metaclass=_RequireAttrsABCMeta):

     and returns a holoviews plot.

     """

-    required_attributes = ["data", "npoints", "pending_points"]

+    data: dict

+    npoints: int

+    pending_points: set

     def tell(self, x, y):

         """Tell the learner about a single value.

@@ -71,11 +71,14 @@ def copy_docstring_from(other):

 class _RequireAttrsABCMeta(abc.ABCMeta):

-    required_attributes = []

-

     def __call__(self, *args, **kwargs):

         obj = super().__call__(*args, **kwargs)

-        for name in obj.required_attributes:

+        for name, type_ in obj.__annotations__.items():

             if not hasattr(obj, name):

                 raise ValueError(f"Required attribute {name} not set in __init__.")

+            elif not isinstance(getattr(obj, name), type_):

+                raise TypeError(

+                    f"The attribute '{name}' is of {type_} instead of {type(getattr(obj, name))}"

+                )

+

         return obj