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.

Upgrade oTree

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

pip3 install -U otree

Create the app

Use your command line to cd to the oTree project folder you created, which contains requirements_base.txt. Assuming you named the folder oTree, you would do:

cd oTree

In this folder, create the public goods app:

otree startapp my_simple_survey

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

Define models.py

Open models.py and scroll to the line that says class Player(BasePlayer):. Here we define the columns for the Player table in the database. Let’s add 2 fields:

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

Note

Python is case-sensitive, so pay attention to which letters are capitalized. Also, make sure to indent your code properly. All lines in a block of code must be aligned along the left edge. When you’re inside a code block (e.g. “if”, “for”, “def”; see below), you need to indent by 4 spaces.

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

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 static otree %}

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

{% block content %}

    Please enter the following information.

    {% formfield player.name %}

    {% formfield player.age %}

    {% next_button %}

{% endblock %}

The second template will be called Results.html.

{% extends "global/Page.html" %}
{% load static otree %}

{% block title %}
    Results
{% endblock %}

{% block content %}

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

    {% next_button %}
{% endblock %}

Define pages.py

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

Since we have 2 templates, we need 2 Page classes in pages.py. 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.

class MyPage(Page):
    form_model = 'player'
    form_fields = ['name', 'age']

Now we define Results. This page doesn’t have a form or any other special attributes, so we just write “pass”.

class Results(Page):
    pass

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

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

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


class MyPage(Page):
    form_model = 'player'
    form_fields = ['name', 'age']


class Results(Page):
    pass


page_sequence = [
    MyPage,
    Results
]

Define the session config in settings.py

Now we go to settings.py in the project’s top folder and add an entry to SESSION_CONFIGS.

SESSION_CONFIGS = [
    {
        'name': 'my_simple_survey',
        'num_demo_participants': 3,
        'app_sequence': ['my_simple_survey'],
    },
    # other session configs go here ...
]

Start the server

Enter:

otree devserver

Then open your browser to http://localhost:8000 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 devserver
Traceback (most recent call last):
  File "C:\oTree\chris\manage.py", line 10, in <module>
    execute_from_command_line(sys.argv, script_file=__file__)
  File "c:\otree\core\otree\management\cli.py", line 170, in execute_from_command_line
    utility.execute()
  File "C:\oTree\venv\lib\site-packages\django\core\management\__init__.py", line 328, in execute
    django.setup()
  File "C:\oTree\venv\lib\site-packages\django\__init__.py", line 18, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "C:\oTree\venv\lib\site-packages\django\apps\registry.py", line 108, in populate
    app_config.import_models(all_models)
  File "C:\oTree\venv\lib\site-packages\django\apps\config.py", line 198, in import_models
    self.models_module = import_module(models_module_name)
  File "C:\Python27\Lib\importlib\__init__.py", line 37, in import_module
    __import__(name)
  File "C:\oTree\chris\public_goods_simple\models.py", line 40
    self.total_contribution = sum([p.contribution for p in self.get_players()])
       ^
IndentationError: expected an indented block

It’s called a “traceback” because it traces the error down through the chain of code. 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\models.py", line 40. So, go to that file & line number. 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). 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/easymoney.py, which is not part of my app, but rather an external package:

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