exe=fluid.Executor(place)
exe.run(fluid.default_startup_program())

在第一次执行到fluid.default_startup_program()的时候会报警：

Warning (from warnings module):
File "D:\MyProgrames\Python378\lib\site-packages\paddle\fluid\executor.py", line 1093
warnings.warn(error_info)
UserWarning: There are no operators in the program to be executed. If you pass Program manually, please use fluid.program_guard to ensure the current Program is being used.

然后再次执行就不报警了，这个是为什么？