Provide more informative error message

Author: zaxtax

pymc/distributions/distribution.py

@@ -322,7 +322,11 @@ def __new__(
         else:
             name = _extract_target_of_assignment(2)
             if name is None:
-                raise TypeError("Name could not be inferred for variable")
+                raise TypeError(
+                    "Name could not be inferred for variable from surrounding "
+                    "context. Pass a name explicitly as the first argument to "
+                    "the Distribution."
+                )
 
         if not isinstance(name, string_types):
             raise TypeError(f"Name needs to be a string but got: {name}")

pymc/tests/distributions/test_distribution.py

@@ -433,6 +433,13 @@ def test_autonaming():
 
 def test_autonaming_noname():
     """Test that autonaming fails if no assignment can be found"""
-    with pytest.raises(TypeError, match="Name could not be inferred for variable"):
+    with pytest.raises(
+        TypeError,
+        match=(
+            "Name could not be inferred for variable from surrounding "
+            "context. Pass a name explicitly as the first argument to "
+            "the Distribution."
+        ),
+    ):
         with pm.Model():
             pm.Normal()