Entrypoints (#300)

* Allow codec registry via entrypoints

* remove debug

* Add release note

* Add test

* Mark required but unused test methods as no cover

* better exception

* Skip test is no entryoints

* Add logging

docs/release.rst

@@ -8,6 +8,9 @@ Unreleased
 
 .. _release_0.9.1:
 
+* Add ability to find codecs via entrypoints
+  By :user:`Martin Durant <martindurant>`, :issue:`290`.
+
 0.9.1
 -----
 

numcodecs/registry.py

@@ -1,8 +1,23 @@
 """The registry module provides some simple convenience functions to enable
 applications to dynamically register and look-up codec classes."""
+import logging
 
-
+logger = logging.getLogger("numcodecs")
 codec_registry = dict()
+entries = {}
+
+
+def run_entrypoints():
+    import entrypoints
+    entries.clear()
+    entries.update(entrypoints.get_group_named("numcodecs.codecs"))
+
+
+try:
+    run_entrypoints()
+except (ImportError, ModuleNotFoundError):  # pragma: no cover
+    # marked "no cover" since we will include entrypoints in test env
+    pass
 
 
 def get_codec(config):
@@ -30,8 +45,13 @@ def get_codec(config):
     codec_id = config.pop('id', None)
     cls = codec_registry.get(codec_id)
     if cls is None:
-        raise ValueError('codec not available: %r' % codec_id)
-    return cls.from_config(config)
+        if codec_id in entries:
+            logger.debug("Auto loading codec '%s' from entrypoint", codec_id)
+            cls = entries[codec_id].load()
+            register_codec(cls, codec_id=codec_id)
+    if cls:
+        return cls.from_config(config)
+    raise ValueError('codec not available: %r' % codec_id)
 
 
 def register_codec(cls, codec_id=None):
@@ -50,4 +70,5 @@ def register_codec(cls, codec_id=None):
     """
     if codec_id is None:
         codec_id = cls.codec_id
+    logger.debug("Registering codec '%s'", codec_id)
     codec_registry[codec_id] = cls

numcodecs/tests/package_with_entrypoint-0.1.dist-info/entry_points.txt

@@ -0,0 +1,2 @@
+[numcodecs.codecs]
+test = package_with_entrypoint:TestCodec

numcodecs/tests/package_with_entrypoint/__init__.py

@@ -0,0 +1,12 @@
+from numcodecs.abc import Codec
+
+
+class TestCodec(Codec):
+
+    codec_id = "test"
+
+    def encode(self, buf):  # pragma: no cover
+        pass
+
+    def decode(self, buf, out=None):  # pragma: no cover
+        pass

numcodecs/tests/test_entrypoints.py

@@ -0,0 +1,25 @@
+import os.path
+import sys
+
+import pytest
+
+import numcodecs.registry
+
+
+here = os.path.abspath(os.path.dirname(__file__))
+pytest.importorskip("entrypoints")
+
+
+@pytest.fixture()
+def set_path():
+    sys.path.append(here)
+    numcodecs.registry.run_entrypoints()
+    yield
+    sys.path.remove(here)
+    numcodecs.registry.run_entrypoints()
+    numcodecs.registry.codec_registry.pop("test")
+
+
+def test_entrypoint_codec(set_path):
+    cls = numcodecs.registry.get_codec({"id": "test"})
+    assert cls.codec_id == "test"

requirements_test.txt

@@ -1,5 +1,6 @@
 coverage
 coveralls
+entrypoints
 flake8
 pytest
 pytest-cov