Python lint: Ruff rules for comprehensions and performance (#512)

Author: cclauss

Diff for: examples/clients/simple-chatbot/mcp_simple_chatbot/main.py

@@ -122,8 +122,10 @@ async def list_tools(self) -> list[Any]:
 
         for item in tools_response:
             if isinstance(item, tuple) and item[0] == "tools":
-                for tool in item[1]:
-                    tools.append(Tool(tool.name, tool.description, tool.inputSchema))
+                tools.extend(
+                    Tool(tool.name, tool.description, tool.inputSchema)
+                    for tool in item[1]
+                )
 
         return tools
 
@@ -282,10 +284,9 @@ def __init__(self, servers: list[Server], llm_client: LLMClient) -> None:
 
     async def cleanup_servers(self) -> None:
         """Clean up all servers properly."""
-        cleanup_tasks = []
-        for server in self.servers:
-            cleanup_tasks.append(asyncio.create_task(server.cleanup()))
-
+        cleanup_tasks = [
+            asyncio.create_task(server.cleanup()) for server in self.servers
+        ]
         if cleanup_tasks:
             try:
                 await asyncio.gather(*cleanup_tasks, return_exceptions=True)

Diff for: pyproject.toml

@@ -89,8 +89,8 @@ venv = ".venv"
 strict = ["src/mcp/**/*.py"]
 
 [tool.ruff.lint]
-select = ["E", "F", "I", "UP"]
-ignore = []
+select = ["C4", "E", "F", "I", "PERF", "UP"]
+ignore = ["PERF203"]
 
 [tool.ruff]
 line-length = 88

Diff for: src/mcp/server/fastmcp/utilities/func_metadata.py

@@ -80,7 +80,7 @@ def pre_parse_json(self, data: dict[str, Any]) -> dict[str, Any]:
         dicts (JSON objects) as JSON strings, which can be pre-parsed here.
         """
         new_data = data.copy()  # Shallow copy
-        for field_name, _field_info in self.arg_model.model_fields.items():
+        for field_name in self.arg_model.model_fields.keys():
             if field_name not in data.keys():
                 continue
             if isinstance(data[field_name], str):

Diff for: tests/issues/test_342_base64_encoding.py

@@ -42,7 +42,7 @@ async def test_server_base64_encoding_issue():
 
     # Create binary data that will definitely result in + and / characters
     # when encoded with standard base64
-    binary_data = bytes([x for x in range(255)] * 4)
+    binary_data = bytes(list(range(255)) * 4)
 
     # Register a resource handler that returns our test data
     @server.read_resource()

Diff for: tests/server/fastmcp/prompts/test_base.py

@@ -38,7 +38,7 @@ async def fn(name: str, age: int = 30) -> str:
             return f"Hello, {name}! You're {age} years old."
 
         prompt = Prompt.from_function(fn)
-        assert await prompt.render(arguments=dict(name="World")) == [
+        assert await prompt.render(arguments={"name": "World"}) == [
             UserMessage(
                 content=TextContent(
                     type="text", text="Hello, World! You're 30 years old."
@@ -53,7 +53,7 @@ async def fn(name: str, age: int = 30) -> str:
 
         prompt = Prompt.from_function(fn)
         with pytest.raises(ValueError):
-            await prompt.render(arguments=dict(age=40))
+            await prompt.render(arguments={"age": 40})
 
     @pytest.mark.anyio
     async def test_fn_returns_message(self):

Diff for: tests/server/fastmcp/servers/test_file_server.py

@@ -115,15 +115,15 @@ async def test_read_resource_file(mcp: FastMCP):
 @pytest.mark.anyio
 async def test_delete_file(mcp: FastMCP, test_dir: Path):
     await mcp.call_tool(
-        "delete_file", arguments=dict(path=str(test_dir / "example.py"))
+        "delete_file", arguments={"path": str(test_dir / "example.py")}
     )
     assert not (test_dir / "example.py").exists()
 
 
 @pytest.mark.anyio
 async def test_delete_file_and_check_resources(mcp: FastMCP, test_dir: Path):
     await mcp.call_tool(
-        "delete_file", arguments=dict(path=str(test_dir / "example.py"))
+        "delete_file", arguments={"path": str(test_dir / "example.py")}
     )
     res_iter = await mcp.read_resource("file://test_dir/example.py")
     res_list = list(res_iter)