@@ -4,7 +4,7 @@ import abc

 from contextlib import suppress

 from copy import deepcopy

-from adaptive.utils import load, save

+from adaptive.utils import load, save, _RequireAttrsABCMeta

 def uses_nth_neighbors(n):

@@ -61,7 +61,7 @@ def uses_nth_neighbors(n):

     return _wrapped

-class BaseLearner(metaclass=abc.ABCMeta):

+class BaseLearner(metaclass=_RequireAttrsABCMeta):

     """Base class for algorithms for learning a function 'f: X → Y'.

     Attributes

@@ -85,6 +85,8 @@ class BaseLearner(metaclass=abc.ABCMeta):

     and returns a holoviews plot.

     """

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

+

     def tell(self, x, y):

         """Tell the learner about a single value.