[GitHub] [airflow] casassg commented on a change in pull request #8652: [AIP-31] Implement XComArg model to functionally pass output from one operator to the next

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

casassg commented on a change in pull request #8652:
URL: https://github.com/apache/airflow/pull/8652#discussion_r420476130



##########
File path: airflow/models/xcom_arg.py
##########
@@ -0,0 +1,147 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+from typing import Any, Dict, List, Union
+
+from airflow.exceptions import AirflowException
+from airflow.models.baseoperator import BaseOperator  # pylint: disable=R0401
+from airflow.models.xcom import XCOM_RETURN_KEY
+
+
+class XComArg:
+    """
+    Class that represents a XCom push from a previous operator.
+    Defaults to "return_value" as only key.
+
+    Current implementations supports
+        xcomarg >> op
+        xcomarg << op
+        op >> xcomarg   (by BaseOperator code)
+        op << xcomarg   (by BaseOperator code)
+
+    **Example**: The moment you get a result from any operator (functional or regular) you can ::
+
+        any_op = AnyOperator()
+        xcomarg = XComArg(any_op) OR xcomarg = any_op.output
+        my_op = MyOperator()
+        my_op >> xcomarg
+
+    This object can be used in legacy Operators via Jinja.
+
+    **Example**: You can make this result to be part of any generated string ::
+
+        any_op = AnyOperator()
+        xcomarg = any_op.output
+        op1 = MyOperator(my_text_message=f"the value is {xcomarg}")
+        op2 = MyOperator(my_text_message=f"the value is {xcomarg['topic']}")
+
+    :param operator: operator to which the XComArg belongs to
+    :type operator: airflow.models.baseoperator.BaseOperator
+    :param key: key value which is used for xcom_pull (key in the XCom table)
+    :type key: str
+    """
+
+    def __init__(self, operator: BaseOperator, key: str = XCOM_RETURN_KEY):
+        self._operator = operator
+        self._key = key
+
+    def __eq__(self, other):
+        return (self.operator == other.operator
+                and self.key == other.key)
+
+    def __lshift__(self, other):
+        """
+        Implements xcomresult << op
+        """
+        self.set_upstream(other)
+        return self
+
+    def __rshift__(self, other):
+        """
+        Implements xcomresult >> op
+        """
+        self.set_downstream(other)
+        return self
+
+    def __getitem__(self, item):
+        """
+        Implements xcomresult['some_result_key']
+        """
+        return XComArg(operator=self.operator, key=item)
+
+    def __str__(self):
+        """
+        Backward compatibility for old-style jinja used in Airflow Operators
+
+        **Example**: to use XArg at BashOperator::
+
+            BashOperator(cmd=f"... { xcomarg } ...")
+
+        :return:
+        """
+        xcom_pull_kwargs = [f"task_ids='{self.operator.task_id}'",
+                            f"dag_id='{self.operator.dag.dag_id}'",
+                            ]
+        if self.key is not None:
+            xcom_pull_kwargs.append(f"key='{self.key}'")

Review comment:
       Wait, didn't we make XCom overwritable instead? I guess you can overwrite it and set it on the `output` property, but not sure if I understand the use for that?




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