Where is the variable error_message defined in django tutorial part 4

Question

The django tutorial part 4 has the following code:

{{ poll.question }}

{% if error_message %}<p><strong>{{ error_message }}</strong></p>{% endif %}

<form action="{% url 'polls:vote' poll.id %}" method="post">
{% csrf_token %}
{% for choice in poll.choice_set.all %}
    <input type="radio" name="choice" id="choice{{ forloop.counter }}" value="{{ choice.id }}"     />
<label for="choice{{ forloop.counter }}">{{ choice.choice_text }}</label><br />
{% endfor %}
<input type="submit" value="Vote" />
</form>

I'm having trouble finding out where the error_message variable in the if conditional statement is defined. Searches on google, stack overflow and the django apis doesnt seem to give any answer on this.

Answer 1

You should check the code below it:

return render(request, 'polls/detail.html', {
    'question': p,
    'error_message': "You didn't select a choice.",
})