[IMPR] solve mypy issues in tools.collections

- add type annotations for SizedKeyCollection.data
- initialize the data dict in __init__ and clear the dict in clear method
- make GeneratorWrapper.generator an abstract generator instead of
  an iterator

Change-Id: I80e0b351ea4a08b68ee0c812c08e555dd570da26
---
M pywikibot/tools/collections.py
1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/pywikibot/tools/collections.py b/pywikibot/tools/collections.py
index e351e55..b3e2bdf 100644
--- a/pywikibot/tools/collections.py
+++ b/pywikibot/tools/collections.py
@@ -1,6 +1,6 @@
 """Collections datatypes."""
 #
-# (C) Pywikibot team, 2014-2022
+# (C) Pywikibot team, 2014-2023
 #
 # Distributed under the terms of the MIT license.
 #
@@ -11,6 +11,7 @@
 from itertools import chain
 from typing import Any
 
+from pywikibot.backports import Dict, List
 from pywikibot.backports import Generator as GeneratorType
 
 
@@ -68,7 +69,8 @@
             with this collection which will be used as key.
         """
         self.keyattr = keyattr
-        self.clear()
+        self.data: Dict[Any, List[Any]] = {}
+        self.size = 0
 
     def __contains__(self, key) -> bool:
         return key in self.data
@@ -120,7 +122,7 @@
 
     def clear(self) -> None:
         """Remove all elements from SizedKeyCollection."""
-        self.data = {}  # defaultdict fails (T282865)
+        self.data.clear()  # defaultdict fails (T282865)
         self.size = 0
 
     def filter(self, key):
@@ -250,7 +252,7 @@
     @abstractmethod
     def generator(self) -> GeneratorType[Any, Any, Any]:
         """Abstract generator property."""
-        return iter(())
+        yield from ()
 
     def send(self, value: Any) -> Any:
         """Return next yielded value from generator or raise StopIteration.

