This webpage assigns consecutive participant numbers to experiments on Pavlovia.
Usage: If your experiment URL is https://pavlovia.org/a/b then use https://moryscarter.com/vespr/pavlovia.php?folder=a&experiment=b&id=c&researcher=d
Inputs id and researcher are optional but can be used to transfer a non-consecutive participant id and a variable that could be used as a password to access the experiment (to ensure that the participant information sheet has been viewed).
In PsychoPy you can use the participant number to assign participants equally to multiple conditions by using:
condition = int(expInfo['participant'])%x where x is the number of conditions. This will assign values 0 to x-1.