Extend PackageMetadata protocol to include the requisite interface, including some way to iterate over the keys and the new json property.

Author: jaraco

importlib_metadata/_adapters.py

@@ -13,6 +13,10 @@ def __new__(cls, orig: email.message.Message):
     def __init__(self, *args, **kwargs):
         pass
 
+    # suppress spurious error from mypy
+    def __iter__(self):
+        return super().__iter__()
+
     @property
     def json(self):
         """

importlib_metadata/_meta.py

@@ -1,5 +1,5 @@
 from ._compat import Protocol
-from typing import Any, List, TypeVar, Union
+from typing import Any, Dict, Iterator, List, TypeVar, Union
 
 
 _T = TypeVar("_T")
@@ -15,10 +15,19 @@ def __contains__(self, item: str) -> bool:
     def __getitem__(self, key: str) -> str:
         ...  # pragma: no cover
 
+    def __iter__(self) -> Iterator[str]:
+        ...  # pragma: no cover
+
     def get_payload(self) -> str:
         ...  # pragma: no cover
 
     def get_all(self, name: str, failobj: _T = ...) -> Union[List[Any], _T]:
         """
         Return all values associated with a possibly multi-valued key.
         """
+
+    @property
+    def json(self) -> Dict[str, Union[str, List[str]]]:
+        """
+        A JSON-compatible form of the metadata.
+        """