Add type hints

This commit only adds type hints and comments and does not make any changes that
should affect runtime.

The type hints added here derive from work done for #1418.

1 files changed, 46 insertions, 16 deletions

diff --git a/rdflib/plugin.py b/rdflib/plugin.py
index 7ae8e29c..c5ffd093 100644
--- a/rdflib/plugin.py
+++ b/rdflib/plugin.py
@@ -36,8 +36,22 @@ from rdflib.query import (
     UpdateProcessor,
 )
 from rdflib.exceptions import Error
-from typing import Type, TypeVar
 import sys
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Dict,
+    Generic,
+    Iterator,
+    Optional,
+    Tuple,
+    Type,
+    TypeVar,
+    overload,
+)
+
+if TYPE_CHECKING:
+    from pkg_resources import EntryPoint
 
 __all__ = ["register", "get", "plugins", "PluginException", "Plugin", "PKGPlugin"]
 
@@ -52,42 +66,47 @@ rdflib_entry_points = {
     "rdf.plugins.updateprocessor": UpdateProcessor,
 }
 
-_plugins = {}
+_plugins: Dict[Tuple[str, Type[Any]], "Plugin"] = {}
 
 
 class PluginException(Error):
     pass
 
 
-class Plugin(object):
-    def __init__(self, name, kind, module_path, class_name):
+PluginT = TypeVar("PluginT")
+
+
+class Plugin(Generic[PluginT]):
+    def __init__(
+        self, name: str, kind: Type[PluginT], module_path: str, class_name: str
+    ):
         self.name = name
         self.kind = kind
         self.module_path = module_path
         self.class_name = class_name
-        self._class = None
+        self._class: Optional[Type[PluginT]] = None
 
-    def getClass(self):
+    def getClass(self) -> Type[PluginT]:
         if self._class is None:
             module = __import__(self.module_path, globals(), locals(), [""])
             self._class = getattr(module, self.class_name)
         return self._class
 
 
-class PKGPlugin(Plugin):
-    def __init__(self, name, kind, ep):
+class PKGPlugin(Plugin[PluginT]):
+    def __init__(self, name: str, kind: Type[PluginT], ep: "EntryPoint"):
         self.name = name
         self.kind = kind
         self.ep = ep
-        self._class = None
+        self._class: Optional[Type[PluginT]] = None
 
-    def getClass(self):
+    def getClass(self) -> Type[PluginT]:
         if self._class is None:
             self._class = self.ep.load()
         return self._class
 
 
-def register(name: str, kind, module_path, class_name):
+def register(name: str, kind: Type[Any], module_path, class_name):
     """
     Register the plugin for (name, kind). The module_path and
     class_name should be the path to a plugin class.
@@ -96,16 +115,13 @@ def register(name: str, kind, module_path, class_name):
     _plugins[(name, kind)] = p
 
 
-PluginT = TypeVar("PluginT")
-
-
 def get(name: str, kind: Type[PluginT]) -> Type[PluginT]:
     """
     Return the class for the specified (name, kind). Raises a
     PluginException if unable to do so.
     """
     try:
-        p = _plugins[(name, kind)]
+        p: Plugin[PluginT] = _plugins[(name, kind)]
     except KeyError:
         raise PluginException("No plugin registered for (%s, %s)" % (name, kind))
     return p.getClass()
@@ -128,7 +144,21 @@ else:
             _plugins[(ep.name, kind)] = PKGPlugin(ep.name, kind, ep)
 
 
-def plugins(name=None, kind=None):
+@overload
+def plugins(
+    name: Optional[str] = ..., kind: Type[PluginT] = ...
+) -> Iterator[Plugin[PluginT]]:
+    ...
+
+
+@overload
+def plugins(name: Optional[str] = ..., kind: None = ...) -> Iterator[Plugin]:
+    ...
+
+
+def plugins(
+    name: Optional[str] = None, kind: Optional[Type[PluginT]] = None
+) -> Iterator[Plugin]:
     """
     A generator of the plugins.