execute_python

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__,
  }