Pages

Each page that your participants see is defined by a Page.

Your page_sequence gives the order of the pages.

If your game has multiple rounds, this sequence will be repeated (see Rounds).

A Page can have any of the following methods and attributes.

is_displayed()

You can define this function to return True if the page should be shown, and False if the page should be skipped. If omitted, the page will be shown.

For example, to only show the page to P2 in each group:

@staticmethod
def is_displayed(player):
    return player.id_in_group == 2

Or only show the page in round 1:

@staticmethod
def is_displayed(player):
    return player.round_number == 1

If you need to repeat the same rule for many pages, use app_after_this_page.

vars_for_template()

Use this to pass variables to the template. Example:

@staticmethod
def vars_for_template(player):
    a = player.num_apples * 10
    return dict(
        a=a,
        b=1 + 1,
    )

Then in the template you can access a and b like this:

Variables {{ a }} and {{ b }} ...

oTree automatically passes the following objects to the template: player, group, subsession, participant, session, and C. You can access them in the template like this: {{ C.BLAH }} or {{ player.blah }}.

If the user refreshes the page, vars_for_template gets re-executed.

before_next_page()

Here you define any code that should be executed after form validation, before the player proceeds to the next page.

If the page is skipped with is_displayed, then before_next_page will be skipped as well.

Example:

@staticmethod
def before_next_page(player, timeout_happened):
    player.tripled_apples = player.num_apples * 3

timeout_seconds

See Timeouts

Wait pages

See Wait pages

Randomizing page sequence

You can randomize the order of pages using rounds. An example is here.

app_after_this_page

To skip entire apps, you can define app_after_this_page. For example, to skip to the next app, you would do:

@staticmethod
def app_after_this_page(player, upcoming_apps):
    if player.whatever:
        return upcoming_apps[0]

upcoming_apps is the remainder of the app_sequence (a list of strings). Therefore, to skip to the last app, you would return upcoming_apps[-1]. Or you could just return a hardcoded string (as long as that string is in upcoming_apps):

@staticmethod
def app_after_this_page(player, upcoming_apps):
    print('upcoming_apps is', upcoming_apps)
    if player.whatever:
        return "public_goods"

If this function doesn’t return anything, the player proceeds to the next page as usual.

Back button

Note

To use this, you must install oTree 6.0

You can now allow participants to click a “Back” button to go to the previous page.

On the Page class, add this attribute:

class MyPage(Page):
    allow_back_button = True

Then in the template, use {{ back_button }} just as you would use {{ next_button }}.

Back button notes

{{ back_button }} is not the same as the browser’s back button. As was the case previously, the user should not click the browser’s back button.
If you use {{ back_button }} on a page with a form, it’s recommended to also use preserve_unsubmitted_inputs = True so that the form will not be lost if the user clicks “back”.

Advanced usage

If you don’t want to use the built-in {{ back_button }}, you can call the back_button() function using JavaScript, e.g. <button type="button" onclick="back_button(1)">...</button>.

Restrictions of back button

Cannot go back through a wait page
Cannot go to a previous app

(These restrictions may be relaxed in future versions of oTree.)