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#      http://www.apache.org/licenses/LICENSE-2.0
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from abc import ABC

DATA_STREAM_STATELESS_FUNCTION_URN = "flink:transform:ds:stateless_function:v1"
DATA_STREAM_STATEFUL_FUNCTION_URN = "flink:transform:ds:stateful_function:v1"


class Operation(ABC):

    def open(self) -> None:
        pass

    def close(self) -> None:
        pass


class OneInputOperation(ABC):

    def process_element(self, value):
        raise NotImplementedError


class TwoInputOperation(ABC):
    def process_element1(self, value):
        raise NotImplementedError

    def process_element2(self, value):
        raise NotImplementedError