Source code for airflow.models.xcom_arg

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from typing import Any, Dict, List, Sequence, Union

from airflow.exceptions import AirflowException
from airflow.models.baseoperator import BaseOperator  # pylint: disable=R0401
from airflow.models.taskmixin import TaskMixin
from airflow.models.xcom import XCOM_RETURN_KEY


[docs]class XComArg(TaskMixin):
    """
    Class that represents a XCom push from a previous operator.
    Defaults to "return_value" as only key.

    Current implementation 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 (decorated or regular) you can ::

        any_op = AnyOperator()
        xcomarg = XComArg(any_op)
        # or equivalently
        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

[docs]    def __eq__(self, other):
        return self.operator == other.operator and self.key == other.key

[docs]    def __getitem__(self, item):
        """Implements xcomresult['some_result_key']"""
        return XComArg(operator=self.operator, key=item)

[docs]    def __str__(self):
        """
        Backward compatibility for old-style jinja used in Airflow Operators

        **Example**: to use XComArg 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}'")

        xcom_pull_kwargs = ", ".join(xcom_pull_kwargs)
        # {{{{ are required for escape {{ in f-string
        xcom_pull = f"{{{{ task_instance.xcom_pull({xcom_pull_kwargs}) }}}}"
        return xcom_pull

    @property
[docs]    def operator(self) -> BaseOperator:
        """Returns operator of this XComArg."""
        return self._operator

    @property
[docs]    def roots(self) -> List[BaseOperator]:
        """Required by TaskMixin"""
        return [self._operator]

    @property
[docs]    def leaves(self) -> List[BaseOperator]:
        """Required by TaskMixin"""
        return [self._operator]

    @property
[docs]    def key(self) -> str:
        """Returns keys of this XComArg"""
        return self._key

[docs]    def set_upstream(self, task_or_task_list: Union[TaskMixin, Sequence[TaskMixin]]):
        """Proxy to underlying operator set_upstream method. Required by TaskMixin."""
        self.operator.set_upstream(task_or_task_list)

[docs]    def set_downstream(self, task_or_task_list: Union[TaskMixin, Sequence[TaskMixin]]):
        """Proxy to underlying operator set_downstream method. Required by TaskMixin."""
        self.operator.set_downstream(task_or_task_list)

[docs]    def resolve(self, context: Dict) -> Any:
        """
        Pull XCom value for the existing arg. This method is run during ``op.execute()``
        in respectable context.
        """
        resolved_value = self.operator.xcom_pull(
            context=context,
            task_ids=[self.operator.task_id],
            key=str(self.key),  # xcom_pull supports only key as str
            dag_id=self.operator.dag.dag_id,
        )
        if not resolved_value:
            raise AirflowException(
                f'XComArg result from {self.operator.task_id} at {self.operator.dag.dag_id} '
                f'with key="{self.key}"" is not found!'
            )
        resolved_value = resolved_value[0]

        return resolved_value