FIX available_if used on an unbound method (scikit-learn#20655)

harupy · web-flow · commit cc8d84a0c136 · 2021-08-05T18:06:30.000+10:00
diff --git a/sklearn/utils/metaestimators.py b/sklearn/utils/metaestimators.py
@@ -100,22 +100,27 @@ def __init__(self, fn, check, attribute_name):
         update_wrapper(self, fn)
 
     def __get__(self, obj, owner=None):
+        attr_err = AttributeError(
+            f"This {repr(owner.__name__)} has no attribute {repr(self.attribute_name)}"
+        )
         if obj is not None:
             # delegate only on instances, not the classes.
             # this is to allow access to the docstrings.
             if not self.check(obj):
-                raise AttributeError(
-                    f"This {repr(owner.__name__)}"
-                    " has no attribute"
-                    f" {repr(self.attribute_name)}"
-                )
+                raise attr_err
 
             # lambda, but not partial, allows help() to work with update_wrapper
             out = lambda *args, **kwargs: self.fn(obj, *args, **kwargs)  # noqa
         else:
+
+            def fn(*args, **kwargs):
+                if not self.check(args[0]):
+                    raise attr_err
+                return self.fn(*args, **kwargs)
+
             # This makes it possible to use the decorated method as an unbound method,
             # for instance when monkeypatching.
-            out = lambda *args, **kwargs: self.fn(*args, **kwargs)  # noqa
+            out = lambda *args, **kwargs: fn(*args, **kwargs)  # noqa
         # update the docstring of the returned function
         update_wrapper(out, self.fn)
         return out
diff --git a/sklearn/utils/tests/test_metaestimators.py b/sklearn/utils/tests/test_metaestimators.py
@@ -1,3 +1,5 @@
+import pytest
+
 from sklearn.utils.metaestimators import if_delegate_has_method
 from sklearn.utils.metaestimators import available_if
 
@@ -105,9 +107,18 @@ def test_available_if():
     assert hasattr(AvailableParameterEstimator(), "available_func")
     assert not hasattr(AvailableParameterEstimator(available=False), "available_func")
 
+
+def test_available_if_unbound_method():
     # This is a non regression test for:
     # https://github.com/scikit-learn/scikit-learn/issues/20614
     # to make sure that decorated functions can be used as an unbound method,
     # for instance when monkeypatching.
     est = AvailableParameterEstimator()
     AvailableParameterEstimator.available_func(est)
+
+    est = AvailableParameterEstimator(available=False)
+    with pytest.raises(
+        AttributeError,
+        match="This 'AvailableParameterEstimator' has no attribute 'available_func'",
+    ):
+        AvailableParameterEstimator.available_func(est)
