Replace Serializer and MediaHandler with protocol

falcon/app.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 """Falcon App class."""
-
+import typing
 from functools import wraps
 from inspect import iscoroutinefunction
 import pathlib
@@ -36,11 +36,12 @@
 from falcon.response import Response
 from falcon.response import ResponseOptions
 import falcon.status_codes as status
-from falcon.typing import ErrorHandler, ErrorSerializer, SinkPrefix
 from falcon.util import deprecation
 from falcon.util import misc
 from falcon.util.misc import code_to_http_status
 
+if typing.TYPE_CHECKING:
+    from falcon.typing import ErrorHandler, ErrorSerializer, SinkPrefix
 
 # PERF(vytas): On Python 3.5+ (including cythonized modules),
 # reference via module global is faster than going via self

falcon/media/base.py

@@ -3,10 +3,9 @@
 from typing import IO, Optional, Union
 
 from falcon.constants import MEDIA_JSON
-from falcon.typing import Serializer
 
 
-class BaseHandler(Serializer, metaclass=abc.ABCMeta):
+class BaseHandler(metaclass=abc.ABCMeta):
     """Abstract Base Class for an internet media type handler."""
 
     # NOTE(kgriffs): The following special methods are used to enable an

falcon/media/handlers.py

@@ -1,3 +1,4 @@
+import typing
 from collections import UserDict
 import functools
 
@@ -10,11 +11,14 @@
 from falcon.media.multipart import MultipartFormHandler
 from falcon.media.multipart import MultipartParseOptions
 from falcon.media.urlencoded import URLEncodedFormHandler
-from falcon.typing import MediaHandlers
 from falcon.util import deprecation
 from falcon.util import misc
 from falcon.vendor import mimeparse
 
+if typing.TYPE_CHECKING:
+    from typing import Mapping
+    from falcon.typing import Serializer
+
 
 class MissingDependencyHandler:
     """Placeholder handler that always raises an error.
@@ -35,13 +39,13 @@ def _raise(self, *args, **kwargs):
     serialize = deserialize = _raise
 
 
-class Handlers(MediaHandlers, UserDict):
+class Handlers(UserDict):
     """A :class:`dict`-like object that manages Internet media type handlers."""
 
     def __init__(self, initial=None):
         self._resolve = self._create_resolver()
 
-        handlers = initial or {
+        handlers: Mapping[str, Serializer] = initial or {
             MEDIA_JSON: JSONHandler(),
             MEDIA_MULTIPART: MultipartFormHandler(),
             MEDIA_URLENCODED: URLEncodedFormHandler(),

falcon/typing.py

@@ -30,21 +30,24 @@
     from falcon.request import Request
     from falcon.response import Response
 
-Link = Dict[str, str]
+    from typing import Protocol
 
+    class Serializer(Protocol):
+        def serialize(
+            self,
+            media: MutableMapping[str, Union[str, int, None, Link]],
+            content_type: str,
+        ) -> bytes:
+            ...
 
-class Serializer:
-    def serialize(
-        self, media: MutableMapping[str, Union[str, int, None, Link]], content_type: str
-    ) -> bytes:
-        raise NotImplementedError()
+    class MediaHandlers(Protocol):
+        def _resolve(
+            self, media_type: str, default: str, raise_not_found: bool = False
+        ) -> Tuple[Serializer, Optional[Callable], Optional[Callable]]:
+            ...
 
 
-class MediaHandlers:
-    def _resolve(
-        self, media_type: str, default: str, raise_not_found: bool = False
-    ) -> Tuple[Serializer, Optional[Callable], Optional[Callable]]:
-        raise NotImplementedError()
+Link = Dict[str, str]
 
 
 # Error handlers