If you are using OS X, download the following installers and follow their instructions:
and, if needed:
Download the Expyriment source (.zip) and install as described here.
Do not start your experiments out of IDLE
If you are using the IDLE editor that comes with the Python installation, be aware that IDLE itself is written in Python. Starting your Expyriment programme out of IDLE (by clicking on “Run” or by pressing F5), might thus lead to improper timing!
We therefore strongly suggest to run Expyriment programmes from the command line if testing subjects.