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from __future__ import annotations
import inspect
from typing import TYPE_CHECKING, Any, Callable, Iterator, Mapping, Sequence, overload
from sqlalchemy import func
from sqlalchemy.orm import Session
from airflow.exceptions import XComNotFound
from airflow.models.abstractoperator import AbstractOperator
from airflow.models.taskmixin import DAGNode, DependencyMixin
from airflow.models.xcom import XCOM_RETURN_KEY
from airflow.utils.context import Context
from airflow.utils.edgemodifier import EdgeModifier
from airflow.utils.session import NEW_SESSION, provide_session
from airflow.utils.types import NOTSET
if TYPE_CHECKING:
from airflow.models.dag import DAG
from airflow.models.operator import Operator
[docs]class XComArg(DependencyMixin):
"""Reference to an XCom value pushed from another operator.
The 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 instance to which the XComArg references.
:param key: Key used to pull the XCom value. Defaults to *XCOM_RETURN_KEY*,
i.e. the referenced operator's return value.
"""
@overload
def __new__(cls: type[XComArg], operator: Operator, key: str = XCOM_RETURN_KEY) -> XComArg:
"""Called when the user writes ``XComArg(...)`` directly."""
@overload
def __new__(cls: type[XComArg]) -> XComArg:
"""Called by Python internals from subclasses."""
def __new__(cls, *args, **kwargs) -> XComArg:
if cls is XComArg:
return PlainXComArg(*args, **kwargs)
return super().__new__(cls)
@staticmethod
[docs] def iter_xcom_args(arg: Any) -> Iterator[XComArg]:
"""Return XComArg instances in an arbitrary value.
Recursively traverse ``arg`` and look for XComArg instances in any
collection objects, and instances with ``template_fields`` set.
"""
if isinstance(arg, XComArg):
yield arg
elif isinstance(arg, (tuple, set, list)):
for elem in arg:
yield from XComArg.iter_xcom_args(elem)
elif isinstance(arg, dict):
for elem in arg.values():
yield from XComArg.iter_xcom_args(elem)
elif isinstance(arg, AbstractOperator):
for elem in arg.template_fields:
yield from XComArg.iter_xcom_args(elem)
@staticmethod
[docs] def apply_upstream_relationship(op: Operator, arg: Any):
"""Set dependency for XComArgs.
This looks for XComArg objects in ``arg`` "deeply" (looking inside
collections objects and classes decorated with ``template_fields``), and
sets the relationship to ``op`` on any found.
"""
for ref in XComArg.iter_xcom_args(arg):
for operator, _ in ref.iter_references():
op.set_upstream(operator)
@property
[docs] def roots(self) -> list[DAGNode]:
"""Required by TaskMixin"""
return [op for op, _ in self.iter_references()]
@property
[docs] def leaves(self) -> list[DAGNode]:
"""Required by TaskMixin"""
return [op for op, _ in self.iter_references()]
[docs] def set_upstream(
self,
task_or_task_list: DependencyMixin | Sequence[DependencyMixin],
edge_modifier: EdgeModifier | None = None,
):
"""Proxy to underlying operator set_upstream method. Required by TaskMixin."""
for operator, _ in self.iter_references():
operator.set_upstream(task_or_task_list, edge_modifier)
[docs] def set_downstream(
self,
task_or_task_list: DependencyMixin | Sequence[DependencyMixin],
edge_modifier: EdgeModifier | None = None,
):
"""Proxy to underlying operator set_downstream method. Required by TaskMixin."""
for operator, _ in self.iter_references():
operator.set_downstream(task_or_task_list, edge_modifier)
def _serialize(self) -> dict[str, Any]:
"""Called by DAG serialization.
The implementation should be the inverse function to ``deserialize``,
returning a data dict converted from this XComArg derivative. DAG
serialization does not call this directly, but ``serialize_xcom_arg``
instead, which adds additional information to dispatch deserialization
to the correct class.
"""
raise NotImplementedError()
@classmethod
def _deserialize(cls, data: dict[str, Any], dag: DAG) -> XComArg:
"""Called when deserializing a DAG.
The implementation should be the inverse function to ``serialize``,
implementing given a data dict converted from this XComArg derivative,
how the original XComArg should be created. DAG serialization relies on
additional information added in ``serialize_xcom_arg`` to dispatch data
dicts to the correct ``_deserialize`` information, so this function does
not need to validate whether the incoming data contains correct keys.
"""
raise NotImplementedError()
[docs] def iter_references(self) -> Iterator[tuple[Operator, str]]:
"""Iterate through (operator, key) references."""
raise NotImplementedError()
[docs] def map(self, f: Callable[[Any], Any]) -> MapXComArg:
return MapXComArg(self, [f])
[docs] def zip(self, *others: XComArg, fillvalue: Any = NOTSET) -> ZipXComArg:
return ZipXComArg([self, *others], fillvalue=fillvalue)
[docs] def get_task_map_length(self, run_id: str, *, session: Session) -> int | None:
"""Inspect length of pushed value for task-mapping.
This is used to determine how many task instances the scheduler should
create for a downstream using this XComArg for task-mapping.
*None* may be returned if the depended XCom has not been pushed.
"""
raise NotImplementedError()
[docs] def resolve(self, context: Context, session: Session = NEW_SESSION) -> Any:
"""Pull XCom value.
This should only be called during ``op.execute()`` in respectable context.
:meta private:
"""
raise NotImplementedError()
[docs]class PlainXComArg(XComArg):
"""Reference to one single XCom without any additional semantics.
This class should not be accessed directly, but only through XComArg. The
class inheritance chain and ``__new__`` is implemented in this slightly
convoluted way because we want to
a. Allow the user to continue using XComArg directly for the simple
semantics (see documentation of the base class for details).
b. Make ``isinstance(thing, XComArg)`` be able to detect all kinds of XCom
references.
c. Not allow many properties of PlainXComArg (including ``__getitem__`` and
``__str__``) to exist on other kinds of XComArg implementations since
they don't make sense.
:meta private:
"""
def __init__(self, operator: Operator, key: str = XCOM_RETURN_KEY):
self.operator = operator
self.key = key
[docs] def __eq__(self, other: Any) -> bool:
if not isinstance(other, PlainXComArg):
return NotImplemented
return self.operator == other.operator and self.key == other.key
[docs] def __getitem__(self, item: str) -> XComArg:
"""Implements xcomresult['some_result_key']"""
if not isinstance(item, str):
raise ValueError(f"XComArg only supports str lookup, received {type(item).__name__}")
return PlainXComArg(operator=self.operator, key=item)
[docs] def __iter__(self):
"""Override iterable protocol to raise error explicitly.
The default ``__iter__`` implementation in Python calls ``__getitem__``
with 0, 1, 2, etc. until it hits an ``IndexError``. This does not work
well with our custom ``__getitem__`` implementation, and results in poor
DAG-writing experience since a misplaced ``*`` expansion would create an
infinite loop consuming the entire DAG parser.
This override catches the error eagerly, so an incorrectly implemented
DAG fails fast and avoids wasting resources on nonsensical iterating.
"""
raise TypeError("'XComArg' object is not iterable")
[docs] def __repr__(self) -> str:
if self.key == XCOM_RETURN_KEY:
return f"XComArg({self.operator!r})"
return f"XComArg({self.operator!r}, {self.key!r})"
[docs] def __str__(self) -> str:
"""
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_id}'",
]
if self.key is not None:
xcom_pull_kwargs.append(f"key='{self.key}'")
xcom_pull_str = ", ".join(xcom_pull_kwargs)
# {{{{ are required for escape {{ in f-string
xcom_pull = f"{{{{ task_instance.xcom_pull({xcom_pull_str}) }}}}"
return xcom_pull
def _serialize(self) -> dict[str, Any]:
return {"task_id": self.operator.task_id, "key": self.key}
@classmethod
def _deserialize(cls, data: dict[str, Any], dag: DAG) -> XComArg:
return cls(dag.get_task(data["task_id"]), data["key"])
[docs] def iter_references(self) -> Iterator[tuple[Operator, str]]:
yield self.operator, self.key
[docs] def map(self, f: Callable[[Any], Any]) -> MapXComArg:
if self.key != XCOM_RETURN_KEY:
raise ValueError("cannot map against non-return XCom")
return super().map(f)
[docs] def zip(self, *others: XComArg, fillvalue: Any = NOTSET) -> ZipXComArg:
if self.key != XCOM_RETURN_KEY:
raise ValueError("cannot map against non-return XCom")
return super().zip(*others, fillvalue=fillvalue)
[docs] def get_task_map_length(self, run_id: str, *, session: Session) -> int | None:
from airflow.models.taskmap import TaskMap
from airflow.models.xcom import XCom
task = self.operator
if task.is_mapped:
query = session.query(func.count(XCom.map_index)).filter(
XCom.dag_id == task.dag_id,
XCom.run_id == run_id,
XCom.task_id == task.task_id,
XCom.map_index >= 0,
XCom.key == XCOM_RETURN_KEY,
)
else:
query = session.query(TaskMap.length).filter(
TaskMap.dag_id == task.dag_id,
TaskMap.run_id == run_id,
TaskMap.task_id == task.task_id,
TaskMap.map_index < 0,
)
return query.scalar()
@provide_session
[docs] def resolve(self, context: Context, session: Session = NEW_SESSION) -> Any:
task_id = self.operator.task_id
result = context["ti"].xcom_pull(task_ids=task_id, key=str(self.key), default=NOTSET, session=session)
if result is not NOTSET:
return result
if self.key == XCOM_RETURN_KEY:
return None
raise XComNotFound(context["ti"].dag_id, task_id, self.key)
class _MapResult(Sequence):
def __init__(self, value: Sequence | dict, callables: Sequence[Callable[[Any], Any]]) -> None:
self.value = value
self.callables = callables
def __getitem__(self, index: Any) -> Any:
value = self.value[index]
for f in self.callables:
value = f(value)
return value
def __len__(self) -> int:
return len(self.value)
[docs]class MapXComArg(XComArg):
"""An XCom reference with ``map()`` call(s) applied.
This is based on an XComArg, but also applies a series of "transforms" that
convert the pulled XCom value.
"""
def __init__(self, arg: XComArg, callables: Sequence[Callable[[Any], Any]]) -> None:
for c in callables:
if getattr(c, "_airflow_is_task_decorator", False):
raise ValueError("map() argument must be a plain function, not a @task operator")
self.arg = arg
self.callables = callables
[docs] def __repr__(self) -> str:
return f"{self.arg!r}.map([{len(self.callables)} functions])"
def _serialize(self) -> dict[str, Any]:
return {
"arg": serialize_xcom_arg(self.arg),
"callables": [inspect.getsource(c) for c in self.callables],
}
@classmethod
def _deserialize(cls, data: dict[str, Any], dag: DAG) -> XComArg:
# We are deliberately NOT deserializing the callables. These are shown
# in the UI, and displaying a function object is useless.
return cls(deserialize_xcom_arg(data["arg"], dag), data["callables"])
[docs] def iter_references(self) -> Iterator[tuple[Operator, str]]:
yield from self.arg.iter_references()
[docs] def map(self, f: Callable[[Any], Any]) -> MapXComArg:
# Flatten arg.map(f1).map(f2) into one MapXComArg.
return MapXComArg(self.arg, [*self.callables, f])
[docs] def get_task_map_length(self, run_id: str, *, session: Session) -> int | None:
return self.arg.get_task_map_length(run_id, session=session)
@provide_session
[docs] def resolve(self, context: Context, session: Session = NEW_SESSION) -> Any:
value = self.arg.resolve(context, session=session)
if not isinstance(value, (Sequence, dict)):
raise ValueError(f"XCom map expects sequence or dict, not {type(value).__name__}")
return _MapResult(value, self.callables)
class _ZipResult(Sequence):
def __init__(self, values: Sequence[Sequence | dict], *, fillvalue: Any = NOTSET) -> None:
self.values = values
self.fillvalue = fillvalue
@staticmethod
def _get_or_fill(container: Sequence | dict, index: Any, fillvalue: Any) -> Any:
try:
return container[index]
except (IndexError, KeyError):
return fillvalue
def __getitem__(self, index: Any) -> Any:
if index >= len(self):
raise IndexError(index)
return tuple(self._get_or_fill(value, index, self.fillvalue) for value in self.values)
def __len__(self) -> int:
lengths = (len(v) for v in self.values)
if self.fillvalue is NOTSET:
return min(lengths)
return max(lengths)
[docs]class ZipXComArg(XComArg):
"""An XCom reference with ``zip()`` applied.
This is constructed from multiple XComArg instances, and presents an
iterable that "zips" them together like the built-in ``zip()`` (and
``itertools.zip_longest()`` if ``fillvalue`` is provided).
"""
def __init__(self, args: Sequence[XComArg], *, fillvalue: Any = NOTSET) -> None:
if not args:
raise ValueError("At least one input is required")
self.args = args
self.fillvalue = fillvalue
[docs] def __repr__(self) -> str:
args_iter = iter(self.args)
first = repr(next(args_iter))
rest = ", ".join(repr(arg) for arg in args_iter)
if self.fillvalue is NOTSET:
return f"{first}.zip({rest})"
return f"{first}.zip({rest}, fillvalue={self.fillvalue!r})"
def _serialize(self) -> dict[str, Any]:
args = [serialize_xcom_arg(arg) for arg in self.args]
if self.fillvalue is NOTSET:
return {"args": args}
return {"args": args, "fillvalue": self.fillvalue}
@classmethod
def _deserialize(cls, data: dict[str, Any], dag: DAG) -> XComArg:
return cls(
[deserialize_xcom_arg(arg, dag) for arg in data["args"]],
fillvalue=data.get("fillvalue", NOTSET),
)
[docs] def iter_references(self) -> Iterator[tuple[Operator, str]]:
for arg in self.args:
yield from arg.iter_references()
[docs] def get_task_map_length(self, run_id: str, *, session: Session) -> int | None:
all_lengths = (arg.get_task_map_length(run_id, session=session) for arg in self.args)
ready_lengths = [length for length in all_lengths if length is not None]
if len(ready_lengths) != len(self.args):
return None # If any of the referenced XComs is not ready, we are not ready either.
if self.fillvalue is NOTSET:
return min(ready_lengths)
return max(ready_lengths)
@provide_session
[docs] def resolve(self, context: Context, session: Session = NEW_SESSION) -> Any:
values = [arg.resolve(context, session=session) for arg in self.args]
for value in values:
if not isinstance(value, (Sequence, dict)):
raise ValueError(f"XCom zip expects sequence or dict, not {type(value).__name__}")
return _ZipResult(values, fillvalue=self.fillvalue)
_XCOM_ARG_TYPES: Mapping[str, type[XComArg]] = {
"": PlainXComArg,
"map": MapXComArg,
"zip": ZipXComArg,
}
[docs]def serialize_xcom_arg(value: XComArg) -> dict[str, Any]:
"""DAG serialization interface."""
key = next(k for k, v in _XCOM_ARG_TYPES.items() if v == type(value))
if key:
return {"type": key, **value._serialize()}
return value._serialize()
[docs]def deserialize_xcom_arg(data: dict[str, Any], dag: DAG) -> XComArg:
"""DAG serialization interface."""
klass = _XCOM_ARG_TYPES[data.get("type", "")]
return klass._deserialize(data, dag)
