Python lint: Ruff rules for pylint and code complexity

Author: cclauss

pyproject.toml

@@ -91,18 +91,35 @@ venvPath = "."
 venv = ".venv"
 strict = ["src/mcp/**/*.py"]
 
-[tool.ruff.lint]
-select = ["C4", "E", "F", "I", "PERF", "UP"]
-ignore = ["PERF203"]
-
 [tool.ruff]
 line-length = 88
 target-version = "py310"
 
+[tool.ruff.lint]
+select = [
+    "C4",    # flake8-comprehensions
+    "C90",   # mccabe
+    "E",     # pycodestyle
+    "F",     # pyflakes
+    "I",     # isort
+    "PERF",  # Perflint
+    "PL",    # Pylint
+    "UP",    # pyupgrade
+]
+ignore = ["PERF203", "PLR0402"]
+mccabe.max-complexity = 24  # Default is 10
+
 [tool.ruff.lint.per-file-ignores]
 "__init__.py" = ["F401"]
 "tests/server/fastmcp/test_func_metadata.py" = ["E501"]
 
+[tool.ruff.lint.pylint]
+allow-magic-value-types = ["bytes", "float", "int", "str"]
+max-args = 20        # Default is 5
+max-branches = 23    # Default is 12
+max-returns = 13      # Default is 6
+max-statements = 99  # Default is 50
+
 [tool.uv.workspace]
 members = ["examples/servers/*"]
 

src/mcp/server/lowlevel/server.py

@@ -83,7 +83,7 @@ async def main():
 from mcp.server.lowlevel.helper_types import ReadResourceContents
 from mcp.server.models import InitializationOptions
 from mcp.server.session import ServerSession
-from mcp.server.stdio import stdio_server as stdio_server
+from mcp.server.stdio import stdio_server as stdio_server  # noqa: PLC0414
 from mcp.shared.context import RequestContext
 from mcp.shared.exceptions import McpError
 from mcp.shared.message import ServerMessageMetadata, SessionMessage

src/mcp/server/streamable_http.py

@@ -859,20 +859,19 @@ async def message_router():
                             if response_id in self._request_streams:
                                 target_request_id = response_id
 
-                        else:
-                            # Extract related_request_id from meta if it exists
-                            if (
-                                session_message.metadata is not None
-                                and isinstance(
-                                    session_message.metadata,
-                                    ServerMessageMetadata,
-                                )
-                                and session_message.metadata.related_request_id
-                                is not None
-                            ):
-                                target_request_id = str(
-                                    session_message.metadata.related_request_id
-                                )
+                        # Extract related_request_id from meta if it exists
+                        elif (
+                            session_message.metadata is not None
+                            and isinstance(
+                                session_message.metadata,
+                                ServerMessageMetadata,
+                            )
+                            and session_message.metadata.related_request_id
+                            is not None
+                        ):
+                            target_request_id = str(
+                                session_message.metadata.related_request_id
+                            )
 
                         request_stream_id = (
                             target_request_id

tests/shared/test_progress_notifications.py

@@ -41,7 +41,7 @@ async def run_server():
                 capabilities=server.get_capabilities(NotificationOptions(), {}),
             ),
         ) as server_session:
-            global serv_sesh
+            global serv_sesh  # noqa: PLW0603
 
             serv_sesh = server_session
             async for message in server_session.incoming_messages: