From 89517123656e2b7af284fb315dd4c2f6c0410ea2 Mon Sep 17 00:00:00 2001
From: michaelj094 <michaeljolly0116@outlook.com>
Date: Fri, 9 Jan 2026 17:42:35 +0000
Subject: [PATCH] Add Pythonic Pipeline pattern using functional composition

---
 README.md                         |  1 +
 patterns/behavioral/pipeline.py   | 98 +++++++++++++++++++++++++++++++
 tests/behavioral/test_pipeline.py | 19 ++++++
 3 files changed, 118 insertions(+)
 create mode 100644 patterns/behavioral/pipeline.py
 create mode 100644 tests/behavioral/test_pipeline.py

diff --git a/README.md b/README.md
index 4d12a2f1..9b1eef68 100644
--- a/README.md
+++ b/README.md
@@ -48,6 +48,7 @@ __Behavioral Patterns__:
 | [mediator](patterns/behavioral/mediator.py) | an object that knows how to connect other objects and act as a proxy |
 | [memento](patterns/behavioral/memento.py) | generate an opaque token that can be used to go back to a previous state |
 | [observer](patterns/behavioral/observer.py) | provide a callback for notification of events/changes to data |
+| [pipeline](patterns/behavioral/pipeline.py) | compose data processing stages |
 | [publish_subscribe](patterns/behavioral/publish_subscribe.py) | a source syndicates events/data to 0+ registered listeners |
 | [registry](patterns/behavioral/registry.py) | keep track of all subclasses of a given class |
 | [servant](patterns/behavioral/servant.py) | provide common functionality to a group of classes without using inheritance |
diff --git a/patterns/behavioral/pipeline.py b/patterns/behavioral/pipeline.py
new file mode 100644
index 00000000..b4a46f48
--- /dev/null
+++ b/patterns/behavioral/pipeline.py
@@ -0,0 +1,98 @@
+"""
+Pipeline / Functional Pipeline (Pythonic)
+
+This implements the Pipeline pattern using a functional approach, 
+where each stage is a callable transforming an iterable. The goal 
+is to demonstrate a Pythonic alternative to class-based pipelines 
+using generators and composition.
+
+TL;DR:
+    Build data processing flows by chaining small functions.
+    In Python, pipelines are best expressed with callables + iterables
+    (often generators), not heavy class hierarchies.
+
+References:
+    - https://martinfowler.com/articles/collection-pipeline/
+    - https://en.wikipedia.org/wiki/Pipeline_(software)
+
+
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Callable, Iterable, Iterator, TypeVar
+
+T = TypeVar("T")
+U = TypeVar("U")
+
+# A stage transforms an Iterable[T] into an Iterable[U].
+Stage = Callable[[Iterable[T]], Iterable[U]]
+
+
+def compose(*stages: Stage) -> Stage:
+    """Compose stages left-to-right into a single stage."""
+    def _composed(data: Iterable):
+        out = data
+        for stage in stages:
+            out = stage(out)
+        return out
+    return _composed
+
+
+@dataclass(frozen=True)
+class Pipeline:
+    """Convenience wrapper around composed stages."""
+    stages: tuple[Stage, ...]
+
+    def __call__(self, data: Iterable[T]) -> Iterable:
+        fn = compose(*self.stages)
+        return fn(data)
+
+    def then(self, stage: Stage) -> "Pipeline":
+        """Return a new Pipeline with an extra stage appended."""
+        return Pipeline(self.stages + (stage,))
+
+
+
+def map_stage(fn: Callable[[T], U]) -> Stage:
+    """Create a mapping stage."""
+    def _stage(data: Iterable[T]) -> Iterator[U]:
+        for item in data:
+            yield fn(item)
+    return _stage
+
+
+def filter_stage(pred: Callable[[T], bool]) -> Stage:
+    """Create a filtering stage."""
+    def _stage(data: Iterable[T]) -> Iterator[T]:
+        for item in data:
+            if pred(item):
+                yield item
+    return _stage
+
+
+def take(n: int) -> Stage:
+    """Take the first n items from the stream."""
+    if n < 0:
+        raise ValueError("n must be >= 0")
+
+    def _stage(data: Iterable[T]) -> Iterator[T]:
+        count = 0
+        for item in data:
+            if count >= n:
+                break
+            yield item
+            count += 1
+    return _stage
+
+
+if __name__ == "__main__":
+    # Example: numbers -> keep evens -> square -> take first 3
+    p = Pipeline((
+        filter_stage(lambda x: x % 2 == 0),
+        map_stage(lambda x: x * x),
+        take(3),
+    ))
+
+    print(list(p(range(100))))  # [0, 4, 16]
diff --git a/tests/behavioral/test_pipeline.py b/tests/behavioral/test_pipeline.py
new file mode 100644
index 00000000..82369c67
--- /dev/null
+++ b/tests/behavioral/test_pipeline.py
@@ -0,0 +1,19 @@
+from patterns.behavioral.pipeline import Pipeline, filter_stage, map_stage, take
+
+
+def test_pipeline_composes_stages_lazily():
+    p = Pipeline((
+        filter_stage(lambda x: x % 2 == 1),
+        map_stage(lambda x: x + 10),
+        take(4),
+    ))
+
+    assert list(p(range(100))) == [11, 13, 15, 17]
+
+
+def test_take_rejects_negative():
+    try:
+        take(-1)
+        assert False, "Expected ValueError"
+    except ValueError:
+        assert True