Can't read serial response using pyserial

Question

Trying to use pyserial to talk to a Korad KD3005P power supply. (Using Python 3.6)

import serial
ser = serial.Serial('/dev/ttyACM0', baudrate=9600, bytesize=8, parity='N', stopbits=1, timeout=1)
ser.write(b'VSET1:2')
ser.write(b'VOUT1?')
response = ser.readline()
print(response)

VSET1:2 sets the voltage to 2 volts

VOUT1? tells the device to return the current voltage.

But all I get from the VOUT1? part seems to be:

b''

Stuff I've checked or tried without success:

• The device works - I can talk to the device and get responses successfully with these commands through a serial terminal like CuteCom
• Pyserial is kinda working - if I run the above program, the VSET1:2 does change the voltage.
• I've tried different timeouts
• I've tried ser.read() instead with various bit lengths
• I've tried putting the read commands in a while loop

Any suggestions?

Answer 1

Oh.

It's a timing thing of some kind. Removing the VSET command or putting a time.sleep() command in between them and voila.. I get a response.

I'm going to mark this resolved but if anyone can enlighten me as to the nuances of this, thanks.