PsychoPy provides an interface to the labjack U3 class with a couple of minor additions.
This is accessible by:
from psychopy.hardware.labjacks import U3
Except for the additional setdata function the U3 class operates exactly as that in the U3 library that labjack provides, documented here:
http://labjack.com/support/labjackpython
Note
To use labjack devices you do need also to install the driver software described on the page above