Use relative imports everywhere, for consistency.

Fix #946.

Author: aaugustin

docs/api/extensions.rst

@@ -13,7 +13,7 @@ Per-Message Deflate
 Abstract classes
 ----------------
 
-.. automodule:: websockets.extensions.base
+.. automodule:: websockets.extensions
 
     .. autoclass:: Extension
         :members:

docs/extensions.rst

@@ -91,9 +91,8 @@ As a consequence, writing an extension requires implementing several classes:
 ``websockets`` provides abstract base classes for extension factories and
 extensions. See the API documentation for details on their methods:
 
-* :class:`~base.ClientExtensionFactory` and
-  :class:`~base.ServerExtensionFactory` for extension factories,
-
-* :class:`~base.Extension` for extensions.
+* :class:`ClientExtensionFactory` and class:`ServerExtensionFactory` for
+  :extension factories,
+* :class:`Extension` for extensions.
 
 

src/websockets/extensions/__init__.py

@@ -0,0 +1,4 @@
+from .base import *
+
+
+__all__ = ["Extension", "ClientExtensionFactory", "ServerExtensionFactory"]

src/websockets/frames.py

@@ -103,7 +103,7 @@ def parse(
         *,
         mask: bool,
         max_size: Optional[int] = None,
-        extensions: Optional[Sequence["websockets.extensions.base.Extension"]] = None,
+        extensions: Optional[Sequence["extensions.Extension"]] = None,
     ) -> Generator[None, None, "Frame"]:
         """
         Read a WebSocket frame.
@@ -172,7 +172,7 @@ def serialize(
         self,
         *,
         mask: bool,
-        extensions: Optional[Sequence["websockets.extensions.base.Extension"]] = None,
+        extensions: Optional[Sequence["extensions.Extension"]] = None,
     ) -> bytes:
         """
         Write a WebSocket frame.
@@ -338,4 +338,4 @@ def check_close(code: int) -> None:
 
 
 # at the bottom to allow circular import, because Extension depends on Frame
-import websockets.extensions.base  # isort:skip # noqa
+from . import extensions  # isort:skip # noqa

src/websockets/legacy/framing.py

@@ -31,7 +31,7 @@ async def read(
         *,
         mask: bool,
         max_size: Optional[int] = None,
-        extensions: Optional[Sequence["websockets.extensions.base.Extension"]] = None,
+        extensions: Optional[Sequence["extensions.Extension"]] = None,
     ) -> "Frame":
         """
         Read a WebSocket frame.
@@ -102,7 +102,7 @@ def write(
         write: Callable[[bytes], Any],
         *,
         mask: bool,
-        extensions: Optional[Sequence["websockets.extensions.base.Extension"]] = None,
+        extensions: Optional[Sequence["extensions.Extension"]] = None,
     ) -> None:
         """
         Write a WebSocket frame.
@@ -132,4 +132,4 @@ def write(
 
 
 # at the bottom to allow circular import, because Extension depends on Frame
-import websockets.extensions.base  # isort:skip # noqa
+from .. import extensions  # isort:skip # noqa