add error messaging around use of get data in templates

Author: zm711

src/spikeinterface/core/analyzer_extension_core.py

@@ -380,7 +380,12 @@ def _set_params(self, ms_before: float = 1.0, ms_after: float = 2.0, operators=N
         assert isinstance(operators, list)
         for operator in operators:
             if isinstance(operator, str):
-                assert operator in ("average", "std", "median", "mad")
+                if operator not in ("average", "std", "median", "mad"):
+                    error_msg = (
+                        f"You have entered an operator {operator} in your `operators` argument which is "
+                        f"not supported. Please use any of ['average', 'std', 'median', 'mad'] instead."
+                    )
+                    raise ValueError(error_msg)
             else:
                 assert isinstance(operator, (list, tuple))
                 assert len(operator) == 2
@@ -549,9 +554,17 @@ def _get_data(self, operator="average", percentile=None, outputs="numpy"):
         if operator != "percentile":
             key = operator
         else:
-            assert percentile is not None, "You must provide percentile=..."
+            assert percentile is not None, "You must provide percentile=... if `operator=percentile`"
             key = f"percentile_{percentile}"
 
+        if key not in self.data.keys():
+            error_msg = (
+                f"You have entered `operator={key}`, but the only operators calculated are "
+                f"{list(self.data.keys())}. Please use one of these as your `operator` in the "
+                f"`get_data` function."
+            )
+            raise ValueError(error_msg)
+
         templates_array = self.data[key]
 
         if outputs == "numpy":