I have no need to stream the data live
Calling ps2000_run_streaming_ns starts the unit streaming data.
The only way know is to keep track of the value returned by ps2000_get_streaming_last_values.
Alternatively, when you call ps2000_run_streaming_ns, you can set auto_stop to true, which causes the driver to collect max_samples and then stop. You can then retrieve the data using ps2000_get_streaming_values. However, if you are going to do this and not call ps2000_get_streaming_last_values, you may as well use block mode.
I hope this helps