A simple plugin system

streamz/core.py

@@ -307,16 +307,18 @@ def wrapped(*args, **kwargs):
     @classmethod
     def register_plugin_entry_point(cls, entry_point, modifier=identity):
         def stub(*args, **kwargs):
+            """ Entrypoints-based streamz plugin. Will be loaded on first call. """
             node = entry_point.load()
             if not issubclass(node, Stream):
                 raise TypeError(
                     f"Error loading {entry_point.name} "
                     f"from module {entry_point.module_name}: "
                     f"{node.__class__.__name__} must be a subclass of Stream"
                 )
-            cls.register_api(
-                modifier=modifier, attribute_name=entry_point.name
-            )(node)
+            if getattr(cls, entry_point.name).__name__ == "stub":
+                cls.register_api(
+                    modifier=modifier, attribute_name=entry_point.name
+                )(node)
             return node(*args, **kwargs)
         cls.register_api(modifier=modifier, attribute_name=entry_point.name)(stub)
 

streamz/tests/test_plugins.py

@@ -1,3 +1,5 @@
+import inspect
+
 import pytest
 from streamz import Source, Stream
 
@@ -31,16 +33,12 @@ def test_register_plugin_entry_point_modifier():
     class test_source(Source):
         pass
 
-    def modifier(fn):
-        fn.__name__ = 'modified_name'
-        return staticmethod(fn)
-
     entry_point = MockEntryPoint("from_test", test_source)
-    Stream.register_plugin_entry_point(entry_point, modifier)
+    Stream.register_plugin_entry_point(entry_point, staticmethod)
 
     Stream.from_test()
 
-    assert Stream.from_test.__name__ == "modified_name"
+    assert inspect.isfunction(Stream().from_test)
 
 
 def test_register_plugin_entry_point_raises():
@@ -53,17 +51,3 @@ class invalid_node:
 
     with pytest.raises(TypeError):
         Stream.test()
-
-
-def test_register_plugin_entry_point_already_registered():
-    @Stream.register_api()
-    class test(Stream):
-        pass
-
-    entry_point = MockEntryPoint("test_double", test, "test_module")
-
-    Stream.register_plugin_entry_point(entry_point)
-
-    assert Stream.test_double.__name__ == "stub"
-    Stream.test_double()
-    assert Stream.test_double.__name__ == "test"