[GitHub] [airflow] ashb commented on a change in pull request #20297: Rename TaskMixin to DependencyMixin

[GitBox <gi...@apache.org>]

ashb commented on a change in pull request #20297:
URL: https://github.com/apache/airflow/pull/20297#discussion_r768968186



##########
File path: airflow/models/taskmixin.py
##########
@@ -15,61 +15,78 @@
 # specific language governing permissions and limitations
 # under the License.
 
+import warnings
 from abc import abstractmethod
 from typing import Sequence, Union
 
+DependencyMixinOrList = Union["DependencyMixin", Sequence["DependencyMixin"]]
 
-class TaskMixin:
-    """
-    Mixing implementing common chain methods like >> and <<.
 
-    In the following functions we use:
-    Task = Union[BaseOperator, XComArg]
-    No type annotations due to cyclic imports.
-    """
+class DependencyMixin:
+    """Mixing implementing common dependency setting methods methods like >> and <<."""
 
     @property
-    def roots(self):
-        """Should return list of root operator List[BaseOperator]"""
+    def roots(self) -> Sequence["DependencyMixin"]:
+        """
+        List of root nodes -- ones with no upstream dependencies.
+
+        a.k.a. the "start" of this sub-graph
+        """
         raise NotImplementedError()
 
     @property
-    def leaves(self):
-        """Should return list of leaf operator List[BaseOperator]"""
+    def leaves(self) -> Sequence["DependencyMixin"]:
+        """
+        List of leaf nodes -- ones with only upstream dependencies.
+
+        a.k.a. the "end" of this sub-graph
+        """
         raise NotImplementedError()
 
     @abstractmethod
-    def set_upstream(self, other: Union["TaskMixin", Sequence["TaskMixin"]]):
+    def set_upstream(self, other: DependencyMixinOrList):

Review comment:
       I'm not 100% sold on this name, but it felt very verbose the number of places we had `Union["TaskMixin", Sequence["TaskMixin"]]` used.
   
   Is this actually any easier to understand, or is the indirection just hiding this and making it harder to grok?




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