[BUG] fix for get_fitted_params in _HeterogenousMetaEstimator (#191)

Upstream version of `sktime` bugfix
sktime/sktime#4633

This fixes a bug in `get_fitted_params` of `_HeterogenousMetaEstimator`, which is at the root of sktime/sktime#4574.

`get_fitted_params` of `_HeterogenousMetaEstimator` was accidentally calling the private interface point of components rather than the public interface point that it should have.

For reviewers: the first call should be to `_get_fitted_params` of the base class, which is correct. Subsequent calls to components should be to the public interface, `get_fitted_params`.

skbase/base/_meta.py

@@ -188,14 +188,16 @@ def _get_params(
         """
         # Set variables that let us use same code for retrieving params or fitted params
         if fitted:
-            method = "_get_fitted_params"
+            method_shallow = "_get_fitted_params"
+            method_public = "get_fitted_params"
             deepkw = {}
         else:
-            method = "get_params"
+            method_shallow = "get_params"
+            method_public = "get_params"
             deepkw = {"deep": deep}
 
         # Get the direct params/fitted params
-        out = getattr(super(), method)(**deepkw)
+        out = getattr(super(), method_shallow)(**deepkw)
 
         if deep and hasattr(self, attr):
             named_objects = getattr(self, attr)
@@ -207,8 +209,15 @@ def _get_params(
             ]
             out.update(named_objects_)
             for name, obj in named_objects_:
-                if hasattr(obj, method):
-                    for key, value in getattr(obj, method)(**deepkw).items():
+                # checks estimator has the method we want to call
+                cond1 = hasattr(obj, method_public)
+                # checks estimator is fitted if calling get_fitted_params
+                is_fitted = hasattr(obj, "is_fitted") and obj.is_fitted
+                # if we call get_params and not get_fitted_params, this is True
+                cond2 = not fitted or is_fitted
+                # check both conditions together
+                if cond1 and cond2:
+                    for key, value in getattr(obj, method_public)(**deepkw).items():
                         out["%s__%s" % (name, key)] = value
         return out