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prefect.utilities.annotations

BaseAnnotation

Bases: namedtuple('BaseAnnotation', field_names='value'), ABC, Generic[T]

Base class for Prefect annotation types.

Inherits from namedtuple for unpacking support in another tools.

Source code in prefect/utilities/annotations.py 
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class BaseAnnotation(
    namedtuple("BaseAnnotation", field_names="value"), ABC, Generic[T]
):
    """
    Base class for Prefect annotation types.

    Inherits from `namedtuple` for unpacking support in another tools.
    """

    def unwrap(self) -> T:
        if sys.version_info < (3, 8):
            # cannot simply return self.value due to recursion error in Python 3.7
            # also _asdict does not follow convention; it's not an internal method
            # https://stackoverflow.com/a/26180604
            return self._asdict()["value"]
        else:
            return self.value

    def rewrap(self, value: T) -> "BaseAnnotation[T]":
        return type(self)(value)

    def __eq__(self, other: object) -> bool:
        if not type(self) == type(other):
            return False
        return self.unwrap() == other.unwrap()

    def __repr__(self) -> str:
        return f"{type(self).__name__}({self.value!r})"

NotSet

Singleton to distinguish None from a value that is not provided by the user.

Source code in prefect/utilities/annotations.py 
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class NotSet:
    """
    Singleton to distinguish `None` from a value that is not provided by the user.
    """

allow_failure

Bases: BaseAnnotation[T]

Wrapper for states or futures.

Indicates that the upstream run for this input can be failed.

Generally, Prefect will not allow a downstream run to start if any of its inputs are failed. This annotation allows you to opt into receiving a failed input downstream.

If the input is from a failed run, the attached exception will be passed to your function.

Source code in prefect/utilities/annotations.py 
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class allow_failure(BaseAnnotation[T]):
    """
    Wrapper for states or futures.

    Indicates that the upstream run for this input can be failed.

    Generally, Prefect will not allow a downstream run to start if any of its inputs
    are failed. This annotation allows you to opt into receiving a failed input
    downstream.

    If the input is from a failed run, the attached exception will be passed to your
    function.
    """

quote

Bases: BaseAnnotation[T]

Simple wrapper to mark an expression as a different type so it will not be coerced by Prefect. For example, if you want to return a state from a flow without having the flow assume that state.

quote will also instruct prefect to ignore introspection of the wrapped object when passed as flow or task parameter. Parameter introspection can be a significant performance hit when the object is a large collection, e.g. a large dictionary or DataFrame, and each element needs to be visited. This will disable task dependency tracking for the wrapped object, but likely will increase performance.

@task
def my_task(df):
    ...

@flow
def my_flow():
    my_task(quote(df))
Source code in prefect/utilities/annotations.py 
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class quote(BaseAnnotation[T]):
    """
    Simple wrapper to mark an expression as a different type so it will not be coerced
    by Prefect. For example, if you want to return a state from a flow without having
    the flow assume that state.

    quote will also instruct prefect to ignore introspection of the wrapped object
    when passed as flow or task parameter. Parameter introspection can be a
    significant performance hit when the object is a large collection,
    e.g. a large dictionary or DataFrame, and each element needs to be visited. This
    will disable task dependency tracking for the wrapped object, but likely will
    increase performance.

    ```
    @task
    def my_task(df):
        ...

    @flow
    def my_flow():
        my_task(quote(df))
    ```
    """

    def unquote(self) -> T:
        return self.unwrap()

unmapped

Bases: BaseAnnotation[T]

Wrapper for iterables.

Indicates that this input should be sent as-is to all runs created during a mapping operation instead of being split.

Source code in prefect/utilities/annotations.py 
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class unmapped(BaseAnnotation[T]):
    """
    Wrapper for iterables.

    Indicates that this input should be sent as-is to all runs created during a mapping
    operation instead of being split.
    """

    def __getitem__(self, _) -> T:
        # Internally, this acts as an infinite array where all items are the same value
        return self.unwrap()