You meant at runtime? or at editing time? Also what controller are you using? CM-550 I suppose? Also where is the other Python running on? On PC or SBC?
If you meant at runtime, below is a post from a user sending/receiving ASCII strings from MATLAB to the CM-550 in MicroPython, please note how he used input() (this MicroPython function is not documented at all by ROBOTIS).
May be you can adapt his technique for your Python setup and during code execution on both Python computing platforms, as I am not aware that the CM-550 can support any kind of file storage like an SD. If you really need to use an SD storage device you may have to think about using an Arduino MKR ZERO with a SD reader installed. It has the appropriate software to read/write into a file, and the MKR ZERO can interface with ROBOTIS actuators fine.