Make mypy happy.

Author: aaugustin

src/websockets/legacy/server.py

@@ -199,10 +199,11 @@ async def handler(self) -> None:
                 elif isinstance(exc, InvalidHandshake):
                     if self.debug:
                         self.logger.debug("! invalid handshake", exc_info=True)
-                    exc_str = f"{exc}"
-                    while exc.__cause__ is not None:
-                        exc = exc.__cause__
-                        exc_str += f"; {exc}"
+                    exc_chain = cast(BaseException, exc)
+                    exc_str = f"{exc_chain}"
+                    while exc_chain.__cause__ is not None:
+                        exc_chain = exc_chain.__cause__
+                        exc_str += f"; {exc_chain}"
                     status, headers, body = (
                         http.HTTPStatus.BAD_REQUEST,
                         Headers(),

src/websockets/server.py

@@ -163,10 +163,11 @@ def accept(self, request: Request) -> Response:
             self.handshake_exc = exc
             if self.debug:
                 self.logger.debug("! invalid handshake", exc_info=True)
-            exc_str = f"{exc}"
-            while exc.__cause__ is not None:
-                exc = exc.__cause__
-                exc_str += f"; {exc}"
+            exc_chain = cast(BaseException, exc)
+            exc_str = f"{exc_chain}"
+            while exc_chain.__cause__ is not None:
+                exc_chain = exc_chain.__cause__
+                exc_str += f"; {exc_chain}"
             return self.reject(
                 http.HTTPStatus.BAD_REQUEST,
                 f"Failed to open a WebSocket connection: {exc_str}.\n",