thecodecrate-pipeline 1.8.0

This package provides a pipeline pattern implementation

TheCodeCrate's Pipeline

This package provides a pipeline pattern implementation.

The implementation is based on the excellent PHP League Pipeline package.

Installation

pip install thecodecrate-pipeline

Pipeline Pattern

The pipeline pattern allows you to easily compose sequential stages by chaining stages.

In this particular implementation the interface consists of two parts:

• StageInterface
• PipelineInterface

A pipeline consists of zero, one, or multiple stages. A pipeline can process a payload. During the processing the payload will be passed to the first stage. From that moment on the resulting value is passed on from stage to stage.

In the simplest form, the execution chain can be represented as a foreach:

result = payload

for stage in stages:
    result = stage(result)

return result

Effectively this is the same as:

result = stage3(stage2(stage1(payload)))

Immutability

Pipelines are implemented as immutable stage chains. When you pipe a new stage, a new pipeline will be created with the added stage. This makes pipelines easy to reuse, and minimizes side-effects.

Usage

Operations in a pipeline, stages, can be anything that satisfies the Callable type-hint. So closures and anything that's invokable is good.

pipeline = Pipeline().pipe(lambda payload: payload * 10)

# Returns 100
await pipeline.process(10)

Type hinting

Use Pipeline[PayloadType] to type hint the payload type.

pipeline = (
    (Pipeline[int]())
    .pipe(lambda payload: payload * 10)
)

# Returns 100
await pipeline.process(10)

Class based stages

Class based stages are also possible. The StageInterface[PayloadType] can be implemented which ensures you have the correct method signature for the __call__ method.

class TimesTwoStage(StageInterface[int]):
    async def __call__(self, payload: int) -> int:
        return payload * 2

class AddOneStage(StageInterface[int]):
    async def __call__(self, payload: int) -> int:
        return payload + 1

pipeline = (
    (Pipeline[int]())
    .pipe(TimesTwoStage())
    .pipe(AddOneStage())
)

# Returns 21
await pipeline.process(10)

Re-usable Pipelines

Because the PipelineInterface is an extension of the StageInterface pipelines can be re-used as stages. This creates a highly composable model to create complex execution patterns while keeping the cognitive load low.

For example, if we'd want to compose a pipeline to process API calls, we'd create something along these lines:

process_api_request = (
    (Pipeline())
    .pipe(ExecuteHttpRequest())
    .pipe(ParseJsonResponse())
)

pipeline = (
    (Pipeline())
    .pipe(ConvertToPsr7Request())
    .pipe(process_api_request)
    .pipe(ConvertToResponseDto())
)

await pipeline.process(DeleteBlogPost(post_id))

Pipeline Builders

Because pipelines themselves are immutable, pipeline builders are introduced to facilitate distributed composition of a pipeline.

The PipelineBuilder[PayloadType] builder collect stages and allow you to create a pipeline at any given time.

pipeline_builder = (
    (PipelineBuilder())
    .add(LogicalStage())
    .add(AnotherStage())
    .add(LastStage())
)

# Build the pipeline
pipeline = pipeline_builder.build()

Declarative Pipeline Stages

You can define pipeline stages declaratively by specifying them as class-level attributes. This makes it easier to set up and reuse pipelines with predefined stages.

Example:

class MyPipeline(Pipeline[int]):
    processor_class = ChainedProcessor
    stages = [
        TimesTwoStage(),
        TimesThreeStage(),
    ]

# Process the payload through the pipeline with the declared stages
result = await MyPipeline().process(5)

# Returns 30

In this example, MyPipeline declares its stages (TimesTwoStage and TimesThreeStage) directly in the class definition, making the pipeline easier to set up and more readable.

This declarative approach allows you to easily reuse pipelines across your project without needing to manually compose them every time.

Exception handling

This package is completely transparent when dealing with exceptions. In no case will this package catch an exception or silence an error. Exceptions should be dealt with on a per-case basis. Either inside a stage or at the time the pipeline processes a payload.

pipeline = Pipeline().pipe(lambda payload: payload / 0)

try:
    await pipeline.process(10)
except ValueError as e:
    # Handle the exception.
    pass