Python REPL MCP Server

Instructions

Implementation Reference

• src/mcp_python/server.py:82-142 (handler)

  Executes the provided Python code in a persistent namespace, captures stdout/stderr, handles reset option, formats output or errors, returns as TextContent.
  if name == "execute_python": code = arguments.get("code") if not code: raise ValueError("Missing code parameter") # Check if we should reset the session if arguments.get("reset", False): self.global_namespace.clear() self.global_namespace["__builtins__"] = __builtins__ return [ types.TextContent( type="text", text="Python session reset. All variables cleared." ) ] # Capture stdout and stderr stdout = io.StringIO() stderr = io.StringIO() try: # Execute code with output redirection with redirect_stdout(stdout), redirect_stderr(stderr): exec(code, self.global_namespace) # Combine output output = stdout.getvalue() errors = stderr.getvalue() # Format response result = "" if output: result += f"Output:\n{output}" if errors: result += f"\nErrors:\n{errors}" if not output and not errors: # Try to get the value of the last expression try: last_line = code.strip().split('\n')[-1] last_value = eval(last_line, self.global_namespace) result = f"Result: {repr(last_value)}" except (SyntaxError, ValueError, NameError): result = "Code executed successfully (no output)" return [ types.TextContent( type="text", text=result ) ] except Exception as e: # noqa: F841 # Capture and format any exceptions error_msg = f"Error executing code:\n{traceback.format_exc()}" return [ types.TextContent( type="text", text=error_msg ) ]
• src/mcp_python/server.py:35-49 (schema)

  Defines the input schema for execute_python tool: required 'code' string, optional 'reset' boolean.
  inputSchema={ "type": "object", "properties": { "code": { "type": "string", "description": "Python code to execute", }, "reset": { "type": "boolean", "description": "Reset the Python session (clear all variables)", "default": False } }, "required": ["code"], },
• src/mcp_python/server.py:32-50 (registration)

  Registers the execute_python tool in the list_tools handler, including name, description, and input schema.
  types.Tool( name="execute_python", description="Execute Python code and return the output. Variables persist between executions.", inputSchema={ "type": "object", "properties": { "code": { "type": "string", "description": "Python code to execute", }, "reset": { "type": "boolean", "description": "Reset the Python session (clear all variables)", "default": False } }, "required": ["code"], }, ),
• src/mcp_python/server.py:16-18 (helper)

  Initializes the shared global namespace used for persistent variable state across execute_python calls.
  self.global_namespace = { "__builtins__": __builtins__, }