Part 0: Simple survey

Let’s create a simple survey – on the first page, we ask the participant for their name and age, then on the next page, display this info back to them.

YouTube version of this tutorial (note: in the video, the app is called helloworld, not my_simple_survey).

Upgrade oTree

To ensure you are using the latest version of oTree, open your command window and run:

pip3 install -U otree-core
otree resetdb

Create the app

Use your command line to cd to the oTree project folder you created, the one that contains requirements_base.txt. If the folder is called oTree, you would do:

cd oTree

In this directory, create the public goods app:

otree startapp my_simple_survey

Then in PyCharm, go to the folder my_simple_survey that was created.


Open and scroll to the line that says class Player(BasePlayer):. Here we can define what fields will be stored in the database for each player. Let’s add 2 fields:

  • name (which is a CharField, meaning text characters)
  • age (which is a positive integer field)
class Player(BasePlayer):
    name = models.CharField()
    age = models.PositiveIntegerField()

Define the template

This survey has 2 pages:

  • Page 1: players enter their name and age
  • Page 2: players see the data they entered on the previous page

In this section we will define the HTML templates that users see.

So, let’s make 2 HTML files under templates/my_simple_survey/.

Let’s name the first page MyPage.html, and put these contents inside:

{% extends "global/Page.html" %}
{% load staticfiles otree_tags %}

{% block title %}
    Enter your information
{% endblock %}

{% block content %}

    {% formfield with label="Enter your name" %}

    {% formfield player.age with label="Enter your age" %}

    {% next_button %}

{% endblock %}

The second template will be called Results.html.

{% extends "global/Page.html" %}
{% load staticfiles otree_tags %}

{% block title %}
{% endblock %}

{% block content %}

    <p>Your name is {{ }} and your age is {{ player.age }}.</p>

    {% next_button %}
{% endblock %}


Now we define our views, which contain the logic for how to display the HTML templates.

Since we have 2 templates, we need 2 Page classes in The names should match those of the templates (MyPage and Results).

First let’s define MyPage. This page contains a form, so we need to define form_model and form_fields. Specifically, this form should let you set the name and age fields on the player.

class MyPage(Page):
    form_model = models.Player
    form_fields = ['name', 'age']

Now we define Results. This page doesn’t have a form so our class definition can just say pass.

class Results(Page):

If already has a WaitPage, you can delete that, because WaitPages are only necessary for multi-player games and more complex games.

Then, set your page_sequence to MyPage followed by Results. So, all in all, should contain this:

from otree.api import Currency as c, currency_range
from . import models
from ._builtin import Page, WaitPage
from .models import Constants

class MyPage(Page):
    form_model = models.Player
    form_fields = ['name', 'age']

class Results(Page):

page_sequence = [

Define the session config in

Now we go to in the project’s root directory and add an entry to SESSION_CONFIGS.

        'name': 'my_simple_survey',
        'display_name': "My Simple Survey",
        'num_demo_participants': 3,
        'app_sequence': ['my_simple_survey'],
    # other session configs go here ...

Reset the database and run


otree resetdb
otree runserver

Then open your browser to to try out the survey.

Fix any errors

If there is an error in your code, the command line will display a “traceback” (error message) that is formatted something like this:

C:\oTree\chris> otree resetdb
Traceback (most recent call last):
  File "C:\oTree\chris\", line 10, in <module>
    execute_from_command_line(sys.argv, script_file=__file__)
  File "c:\otree\core\otree\management\", line 170, in execute_from_command_line
  File "C:\oTree\venv\lib\site-packages\django\core\management\", line 328, in execute
  File "C:\oTree\venv\lib\site-packages\django\", line 18, in setup
  File "C:\oTree\venv\lib\site-packages\django\apps\", line 108, in populate
  File "C:\oTree\venv\lib\site-packages\django\apps\", line 198, in import_models
    self.models_module = import_module(models_module_name)
  File "C:\Python27\Lib\importlib\", line 37, in import_module
  File "C:\oTree\chris\public_goods_simple\", line 40
    self.total_contribution = sum([p.contribution for p in self.get_players()])
IndentationError: expected an indented block

Your first step should be to look at the last lines of the message. Specifically, find the file and line number of the last entry. In the above example, it’s "C:\oTree\chris\public_goods_simple\", line 40. Open that file and go to that line number to see if there is a problem there. Specifically, look for the problem mentioned at the last line of the traceback. In this example, it is IndentationError: expected an indented block (which indicates that the problem has to do with code indentation). Python editors like PyCharm usually underline errors in red to make them easier to find. Try to fix the error then run the command again.

Sometimes the last line of the traceback refers to a file that is not part of your code. For example, in the below traceback, the last line refers to /site-packages/, which is not part of my app, but rather an external package:

File "/usr/local/lib/python3.5/site-packages/django/core/handlers/" in get_response
  132.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/usr/local/lib/python3.5/site-packages/django/views/generic/" in view
  71.             return self.dispatch(request, *args, **kwargs)
File "/usr/local/lib/python3.5/site-packages/django/utils/" in _wrapper
  34.             return bound_func(*args, **kwargs)
File "/usr/local/lib/python3.5/site-packages/django/views/decorators/" in _wrapped_view_func
  57.         response = view_func(request, *args, **kwargs)
File "/usr/local/lib/python3.5/site-packages/django/utils/" in bound_func
  30.                 return func.__get__(self, type(self))(*args2, **kwargs2)
File "/usr/local/lib/python3.5/site-packages/django/utils/" in _wrapper
  34.             return bound_func(*args, **kwargs)
File "/usr/local/lib/python3.5/site-packages/django/views/decorators/" in _cache_controlled
  43.             response = viewfunc(request, *args, **kw)
File "/usr/local/lib/python3.5/site-packages/django/utils/" in bound_func
  30.                 return func.__get__(self, type(self))(*args2, **kwargs2)
File "/usr/local/lib/python3.5/site-packages/otree/views/" in dispatch
  315.                 request, *args, **kwargs)
File "/usr/local/lib/python3.5/site-packages/django/views/generic/" in dispatch
  89.         return handler(request, *args, **kwargs)
File "/usr/local/lib/python3.5/site-packages/otree/views/" in get
  814.         return super(FormPageMixin, self).get(request, *args, **kwargs)
File "/usr/local/lib/python3.5/site-packages/vanilla/" in get
  294.         context = self.get_context_data(form=form)
File "/usr/local/lib/python3.5/site-packages/otree/views/" in get_context_data
  193.         vars_for_template = self.resolve_vars_for_template()
File "/usr/local/lib/python3.5/site-packages/otree/views/" in resolve_vars_for_template
  212.         context.update(self.vars_for_template() or {})
File "/Users/chris/oTree/public_goods/" in vars_for_template
  108.             'total_payoff': self.player.payoff + Constants.fixed_pay}
File "/usr/local/lib/python3.5/site-packages/" in <lambda>
  36.     return lambda self, other, context=None: self.__class__(method(self, _to_decimal(other)))
File "/usr/local/lib/python3.5/site-packages/" in _to_decimal
  24.         return Decimal(amount)

Exception Type: TypeError at /p/j0p7dxqo/public_goods/ResultsFinal/8/
Exception Value: conversion from NoneType to Decimal is not supported

In these situations, look to see if any of your code is contained in the traceback. Above we can see that the traceback goes through the file /Users/chris/oTree/public_goods/, which is part of my project. The bug is on line 108, as indicated.

If you can’t figure out the cause of the error, you can ask a question on the oTree discussion group.