#1 by zahra_rahmani
I want to have a quota for my participants and found this helpful forum post: https://groups.google.com/g/otree/c/E6BbIS64VRE/m/1pcmx-O9AQAJ It tells me to define a session variable, set it to zero initially and then increment it each time a participant fulfills a condition. However, I am stuck at step 2: How/ where can I initialize a session field? Thanks a lot for your help!
#2 by BonnEconLab (edited )
See https://otree.readthedocs.io/en/latest/rounds.html#session-fields. The documentation is quite sparse, though. The following should work: For example, you could add SESSION_FIELDS = [ 'num_participants_finished_intro', 'num_participants_finished_decisions', 'num_participants_finished_experiment', ] to your settings.py file. You should then be able to increment session.vars['num_participants_finished_intro'] etc. depending on the respective conditions.
#3 by BonnEconLab
To be clear, you will probably have to write player.session.vars['num_participants_finished_intro'] = 0 etc. (not only session.vars['num_participants_finished_intro'] = 0 etc.).
#4 by zahra_rahmani
Thank you very much for your help! Yes, I was unsure about where to set it to zero because I wanted to avoid that it would be resetted to zero for each player/participant. I now implemented the following in my init.py file and it seems to work okay after some testing: def creating_session(subsession: Subsession): for player in subsession.get_players(): if subsession.round_number == 1: subsession.session.countCondition = 0
#5 by BonnEconLab
I’m glad that it works. The following – simpler – code should also do it: def creating_session(subsession): if subsession.round_number == 1: subsession.session.countCondition = 0
#6 by BonnEconLab (edited )
Ah, just one caveat: Be careful where exactly you increment the counter! Say, you intended to use vars_for_template for incrementing your counter, like this: @staticmethod def vars_for_template(player): player.subsession.session.countCondition = player.subsession.session.countCondition + 1 Then the counter would be incremented each time a participant refreshes the respective page. This is probably not what you want, unless you use a dedicated page for this single purpose that is shown, say, for a mere second. Better places are probably after_all_players_arrive(subsession) on a wait page or before_next_page(player) on a welcome page.
#7 by zahra_rahmani
That is an important comment, thank you! I currently increment it in an "is_displayed" function of a page, and I it seems safe when I test it, but I wonder if you think that this is not a good position? class sorryFull(Page): form_model = 'player' @staticmethod def is_displayed(player: Player): countCondition = player.countCondition==1 limit = 15 if (countCondition == True): player.session.vars['countCondition'] += 1 return player.session.vars['countCondition'] > limit else: return False
#8 by BonnEconLab
Hmmm, no I don’t think that including it in is_displayed is safe. I did a quick test: is_displayed is also executed repeatedly whenever I refresh the respective page. To my knowledge, that does not apply to before_next_page. So, I would include a welcome page before your “sorryFull“ page and add before_next_page(player) to the welcome page to increment the counter.