turbaszek commented on a change in pull request #8962:
URL: https://github.com/apache/airflow/pull/8962#discussion_r429151128



##########
File path: airflow/operators/python.py
##########
@@ -145,6 +147,141 @@ def execute_callable(self):
         return self.python_callable(*self.op_args, **self.op_kwargs)
 
 
+class _PythonFunctionalOperator(BaseOperator):
+    """
+    Wraps a Python callable and captures args/kwargs when called for execution.
+
+    :param python_callable: A reference to an object that is callable
+    :type python_callable: python callable
+    :param multiple_outputs: if set, function return value will be
+        unrolled to multiple XCom values. List/Tuples will unroll to xcom 
values
+        with index as key. Dict will unroll to xcom values with keys as keys.
+        Defaults to False.
+    :type multiple_outputs: bool
+    """
+
+    template_fields = ('_op_args', '_op_kwargs')
+    ui_color = '#ffefeb'
+
+    # since we won't mutate the arguments, we should just do the shallow copy
+    # there are some cases we can't deepcopy the objects(e.g protobuf).
+    shallow_copy_attrs = ('python_callable',)
+
+    @apply_defaults
+    def __init__(
+        self,
+        python_callable: Callable,
+        multiple_outputs: bool = False,
+        *args,
+        **kwargs
+    ) -> None:
+        # Check if we need to generate a new task_id
+        task_id = kwargs.get('task_id', None)
+        dag = kwargs.get('dag', None) or DagContext.get_current_dag()
+        if task_id and dag and task_id in dag.task_ids:
+            prefix = task_id.rsplit("__", 1)[0]
+            task_id = sorted(
+                filter(lambda x: x.startswith(prefix), dag.task_ids),
+                reverse=True
+            )[0]
+            num = int(task_id[-1] if '__' in task_id else '0') + 1
+            kwargs['task_id'] = f'{prefix}__{num}'
+
+        if not kwargs.get('do_xcom_push', True) and not multiple_outputs:
+            raise AirflowException('@task needs to have either 
do_xcom_push=True or '
+                                   'multiple_outputs=True.')
+        if not callable(python_callable):
+            raise AirflowException('`python_callable` param must be callable')
+        self._fail_if_method(python_callable)
+        super().__init__(*args, **kwargs)
+        self.python_callable = python_callable
+        self.multiple_outputs = multiple_outputs
+        self._kwargs = kwargs
+        self._op_args: List[Any] = []
+        self._called = False
+        self._op_kwargs: Dict[str, Any] = {}
+
+    @staticmethod
+    def _fail_if_method(python_callable):
+        if 'self' in signature(python_callable).parameters.keys():
+            raise AirflowException('@task does not support methods')
+
+    def __call__(self, *args, **kwargs):
+        # If args/kwargs are set, then operator has been called. Raise 
exception
+        if self._called:

Review comment:
       Do I correctly understand that this will not work?
   ``` python
   @task 
   def update_user(user_id: str):
       ...
   
   with DAG(...):
       # Fetch list of users 
       ...
       # Execute task for each user
       for user_id in users_list:
           update_user(user_id)
   ```

##########
File path: airflow/operators/python.py
##########
@@ -145,6 +148,142 @@ def execute_callable(self):
         return self.python_callable(*self.op_args, **self.op_kwargs)
 
 
+class _PythonFunctionalOperator(BaseOperator):
+    """
+    Wraps a Python callable and captures args/kwargs when called for execution.
+
+    :param python_callable: A reference to an object that is callable
+    :type python_callable: python callable
+    :param multiple_outputs: if set, function return value will be
+        unrolled to multiple XCom values. List/Tuples will unroll to xcom 
values
+        with index as key. Dict will unroll to xcom values with keys as keys.
+        Defaults to False.
+    :type multiple_outputs: bool
+    """
+
+    template_fields = ('_op_args', '_op_kwargs')
+    ui_color = '#ffefeb'
+
+    # since we won't mutate the arguments, we should just do the shallow copy
+    # there are some cases we can't deepcopy the objects(e.g protobuf).
+    shallow_copy_attrs = ('python_callable',)
+
+    @apply_defaults
+    def __init__(
+        self,
+        python_callable: Callable,
+        multiple_outputs: bool = False,
+        *args,
+        **kwargs
+    ) -> None:
+        dag = kwargs.get('dag', None) or DagContext.get_current_dag()
+        kwargs['task_id'] = self._get_unique_task_id(kwargs['task_id'], dag)
+        self._validate_python_callable(python_callable)
+        super().__init__(*args, **kwargs)
+        self.python_callable = python_callable
+        self.multiple_outputs = multiple_outputs
+        self._kwargs = kwargs
+        self._op_args: List[Any] = []
+        self._called = False
+        self._op_kwargs: Dict[str, Any] = {}
+
+    @staticmethod
+    def _get_unique_task_id(task_id, dag):
+        if not dag or task_id not in dag.task_ids:
+            return task_id
+        core = re.split(r'__\d+$', task_id)[0]
+        suffixes = sorted(
+            [int(re.split(r'^.+__', task_id)[1])
+             for task_id in dag.task_ids
+             if re.match(rf'^{core}__\d+$', task_id)]
+        )
+        if not suffixes:
+            return f'{core}__1'
+        return f'{core}__{suffixes[-1] + 1}'
+
+    @staticmethod
+    def _validate_python_callable(python_callable):
+        if not callable(python_callable):
+            raise AirflowException('`python_callable` param must be callable')
+        if 'self' in signature(python_callable).parameters.keys():
+            raise AirflowException('@task does not support methods')
+
+    def __call__(self, *args, **kwargs):
+        # If args/kwargs are set, then operator has been called. Raise 
exception
+        if self._called:
+            raise AirflowException('@task decorated functions can only be 
called once. If you need to reuse '
+                                   'it several times in a DAG, use the `copy` 
method.')
+
+        # If we have no DAG, reinitialize class to capture DAGContext and DAG 
default args.
+        if not self.has_dag():
+            self.__init__(python_callable=self.python_callable,
+                          multiple_outputs=self.multiple_outputs,
+                          **self._kwargs)
+
+        # Capture args/kwargs
+        self._op_args = args
+        self._op_kwargs = kwargs
+        self._called = True
+        return XComArg(self)
+
+    def copy(self, task_id: Optional[str] = None, **kwargs):
+        """
+        Create a copy of the task, allow to overwrite ctor kwargs if needed.
+
+        If alias is created a new DAGContext, apply defaults and set new DAG 
as the operator DAG.
+
+        :param task_id: Task id for the new operator
+        :type task_id: Optional[str]
+        """
+        if task_id:
+            self._kwargs['task_id'] = task_id
+        return _PythonFunctionalOperator(
+            python_callable=self.python_callable,
+            multiple_outputs=self.multiple_outputs,
+            **{**kwargs, **self._kwargs}
+        )
+
+    def execute(self, context: Dict):
+        return_value = self.python_callable(*self._op_args, **self._op_kwargs)
+        self.log.info("Done. Returned value was: %s", return_value)
+        if not self.multiple_outputs:
+            return return_value
+        if isinstance(return_value, dict):
+            for key, value in return_value.items():
+                self.xcom_push(context, str(key), value)
+        elif isinstance(return_value, (list, tuple)):
+            for key, value in enumerate(return_value):
+                self.xcom_push(context, str(key), value)
+        return return_value
+
+
+def task(python_callable: Optional[Callable] = None, **kwargs):
+    """
+    Python operator decorator. Wraps a function into an Airflow operator.
+    Accepts kwargs for operator kwarg. Will try to wrap operator into DAG at 
declaration or
+    on function invocation. Use alias to reuse function in the DAG.
+
+    :param python_callable: Function to decorate
+    :type python_callable: Optional[Callable]
+    :param multiple_outputs: if set, function return value will be
+        unrolled to multiple XCom values. List/Tuples will unroll to xcom 
values
+        with index as key. Dict will unroll to xcom values with keys as keys.
+        Defaults to False.
+    :type multiple_outputs: bool
+
+    """
+    def wrapper(f):
+        """Python wrapper to generate PythonFunctionalOperator out of simple 
python functions.

Review comment:
       ```suggestion
           """
           Python wrapper to generate PythonFunctionalOperator out of simple 
python functions.
   ```

##########
File path: airflow/operators/python.py
##########
@@ -145,6 +147,141 @@ def execute_callable(self):
         return self.python_callable(*self.op_args, **self.op_kwargs)
 
 
+class _PythonFunctionalOperator(BaseOperator):
+    """
+    Wraps a Python callable and captures args/kwargs when called for execution.
+
+    :param python_callable: A reference to an object that is callable
+    :type python_callable: python callable
+    :param multiple_outputs: if set, function return value will be
+        unrolled to multiple XCom values. List/Tuples will unroll to xcom 
values
+        with index as key. Dict will unroll to xcom values with keys as keys.
+        Defaults to False.
+    :type multiple_outputs: bool
+    """
+
+    template_fields = ('_op_args', '_op_kwargs')
+    ui_color = '#ffefeb'
+
+    # since we won't mutate the arguments, we should just do the shallow copy
+    # there are some cases we can't deepcopy the objects(e.g protobuf).
+    shallow_copy_attrs = ('python_callable',)
+
+    @apply_defaults
+    def __init__(
+        self,
+        python_callable: Callable,
+        multiple_outputs: bool = False,
+        *args,
+        **kwargs
+    ) -> None:
+        # Check if we need to generate a new task_id
+        task_id = kwargs.get('task_id', None)
+        dag = kwargs.get('dag', None) or DagContext.get_current_dag()
+        if task_id and dag and task_id in dag.task_ids:
+            prefix = task_id.rsplit("__", 1)[0]
+            task_id = sorted(
+                filter(lambda x: x.startswith(prefix), dag.task_ids),
+                reverse=True
+            )[0]
+            num = int(task_id[-1] if '__' in task_id else '0') + 1
+            kwargs['task_id'] = f'{prefix}__{num}'
+
+        if not kwargs.get('do_xcom_push', True) and not multiple_outputs:
+            raise AirflowException('@task needs to have either 
do_xcom_push=True or '
+                                   'multiple_outputs=True.')
+        if not callable(python_callable):
+            raise AirflowException('`python_callable` param must be callable')
+        self._fail_if_method(python_callable)
+        super().__init__(*args, **kwargs)
+        self.python_callable = python_callable
+        self.multiple_outputs = multiple_outputs
+        self._kwargs = kwargs
+        self._op_args: List[Any] = []
+        self._called = False
+        self._op_kwargs: Dict[str, Any] = {}
+
+    @staticmethod
+    def _fail_if_method(python_callable):
+        if 'self' in signature(python_callable).parameters.keys():
+            raise AirflowException('@task does not support methods')
+
+    def __call__(self, *args, **kwargs):
+        # If args/kwargs are set, then operator has been called. Raise 
exception
+        if self._called:
+            raise AirflowException('@task decorated functions can only be 
called once. If you need to reuse '
+                                   'it several times in a DAG, use the `copy` 
method.')
+
+        # If we have no DAG, reinitialize class to capture DAGContext and DAG 
default args.
+        if not self.has_dag():
+            self.__init__(python_callable=self.python_callable,
+                          multiple_outputs=self.multiple_outputs,
+                          **self._kwargs)
+
+        # Capture args/kwargs
+        self._op_args = args
+        self._op_kwargs = kwargs
+        self._called = True
+        return XComArg(self)
+
+    def copy(self, task_id: Optional[str] = None, **kwargs):
+        """
+        Create a copy of the task, allow to overwrite ctor kwargs if needed.
+
+        If alias is created a new DAGContext, apply defaults and set new DAG 
as the operator DAG.
+
+        :param task_id: Task id for the new operator
+        :type task_id: Optional[str]
+        """
+        if task_id:
+            self._kwargs['task_id'] = task_id
+        return _PythonFunctionalOperator(
+            python_callable=self.python_callable,
+            multiple_outputs=self.multiple_outputs,
+            **{**kwargs, **self._kwargs}
+        )
+
+    def execute(self, context: Dict):
+        return_value = self.python_callable(*self._op_args, **self._op_kwargs)
+        self.log.info("Done. Returned value was: %s", return_value)
+        if not self.multiple_outputs:
+            return return_value
+        if isinstance(return_value, dict):
+            for key, value in return_value.items():
+                self.xcom_push(context, str(key), value)
+        elif isinstance(return_value, (list, tuple)):
+            for key, value in enumerate(return_value):
+                self.xcom_push(context, str(key), value)
+        return return_value
+
+
+def task(python_callable: Optional[Callable] = None, **kwargs):
+    """
+    Python operator decorator. Wraps a function into an Airflow operator.
+    Accepts kwargs for operator kwarg. Will try to wrap operator into DAG at 
declaration or
+    on function invocation. Use alias to reuse function in the DAG.
+
+    :param python_callable: Function to decorate
+    :type python_callable: Optional[Callable]
+    :param multiple_outputs: if set, function return value will be

Review comment:
       Personally I would prefer to use typehints to indicate multiple output 
than a flag. It will solve the issue and add more information to task 
definitions. Of course, typehints are optional but we can require them to make 
multiple outputs work. Here's a similar thing from PySpark:
   
   
https://databricks.com/blog/2020/05/20/new-pandas-udfs-and-python-type-hints-in-the-upcoming-release-of-apache-spark-3-0.html

##########
File path: airflow/operators/python.py
##########
@@ -145,6 +148,142 @@ def execute_callable(self):
         return self.python_callable(*self.op_args, **self.op_kwargs)
 
 
+class _PythonFunctionalOperator(BaseOperator):
+    """
+    Wraps a Python callable and captures args/kwargs when called for execution.
+
+    :param python_callable: A reference to an object that is callable
+    :type python_callable: python callable
+    :param multiple_outputs: if set, function return value will be
+        unrolled to multiple XCom values. List/Tuples will unroll to xcom 
values
+        with index as key. Dict will unroll to xcom values with keys as keys.
+        Defaults to False.
+    :type multiple_outputs: bool
+    """
+
+    template_fields = ('_op_args', '_op_kwargs')
+    ui_color = '#ffefeb'
+
+    # since we won't mutate the arguments, we should just do the shallow copy
+    # there are some cases we can't deepcopy the objects(e.g protobuf).
+    shallow_copy_attrs = ('python_callable',)
+
+    @apply_defaults
+    def __init__(
+        self,
+        python_callable: Callable,
+        multiple_outputs: bool = False,
+        *args,
+        **kwargs
+    ) -> None:
+        dag = kwargs.get('dag', None) or DagContext.get_current_dag()
+        kwargs['task_id'] = self._get_unique_task_id(kwargs['task_id'], dag)
+        self._validate_python_callable(python_callable)
+        super().__init__(*args, **kwargs)
+        self.python_callable = python_callable
+        self.multiple_outputs = multiple_outputs
+        self._kwargs = kwargs
+        self._op_args: List[Any] = []
+        self._called = False
+        self._op_kwargs: Dict[str, Any] = {}
+
+    @staticmethod
+    def _get_unique_task_id(task_id, dag):

Review comment:
       ```suggestion
       def _get_unique_task_id(task_id: str, dag: DAG) -> str:
   ```

##########
File path: airflow/ti_deps/deps/trigger_rule_dep.py
##########
@@ -18,10 +18,10 @@
 
 from collections import Counter
 
-import airflow
 from airflow.ti_deps.deps.base_ti_dep import BaseTIDep
 from airflow.utils.session import provide_session
 from airflow.utils.state import State
+from airflow.utils.trigger_rule import TriggerRule as TR

Review comment:
       Is this a related change? 




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