Question

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Django template can’t loop defaultdict

I am wondering why my defaultdict(list) will show when I test it in my views.py but when I go to show the data on my template, I get nothing, not even an error.

Any suggestions?

Here is my views.py – confirm_list is my defaultdict(list)

def confirmations_report(request, *args, **kwargs):
from investments.models import Investment, InvestmentManager
from reports.forms import ConfirmationsForm
from collections import defaultdict
import ho.pisa as pisa
import cStringIO as StringIO
import os.path
confirm_list = defaultdict(list)
context = {}

if request.POST:
    form = ConfirmationsForm(request.POST)
    if form.is_valid():
        start_date = form.cleaned_data['start_date']
        end_date = form.cleaned_data['end_date']
        investments = Investment.objects.all().filter(contract_no = "",maturity_date__range=(start_date, end_date)).order_by('financial_institution')
        for i in investments:
            confirm_list[i.financial_institution.pk].append({
                'fi':i.financial_institution,
                'fi_address1': i.financial_institution.address1,
                'fi_address2': i.financial_institution.address2,
                'fi_city': i.financial_institution.city,
                'fi_prov': i.financial_institution.state_prov,
                'fi_country': i.financial_institution.country,
                'fi_postal': i.financial_institution.postal,
                'primary_owner': i.plan.get_primary_owner().member,
                'sin': i.plan.get_primary_owner().member.client.sin,
                'type': i.product.code,
                'purchase_amount': i.amount,
                'purchase_date': i.start_date,
            })
            context['investments'] = investments
        context['confirmlist'] = confirm_list
        for key, value in confirm_list.items():
            print key, value
        context['inv'] = investments
    if request.POST.has_key('print_report_submit'):
        context['show_report'] = True
        context['mb_logo'] = os.path.join(os.path.dirname(__file__), "../../../media/images/mb_logo.jpg")
        html = render_to_string('reports/admin/confirm_report_print.html', RequestContext(request,context))
        result = StringIO.StringIO()
        pdf = pisa.pisaDocument(StringIO.StringIO(html.encode("ISO-8859-1")), result)
        response = HttpResponse(result.getvalue(), mimetype='application/pdf')
        response['Content-Disposition'] = 'attachment; filename=unreceived-confirmations.pdf'
        return response

else:
    form = ConfirmationsForm()

context['form'] = form
return render_to_response('reports/admin/confirm_report.html', RequestContext(request, context))

But when I do:

for key, value in confirm_list.items():
            print key, value

On my template like so:

{% extends 'reports/admin/base.html' %}
{% load humanize %}

{% block report_html %}
<h3>Unreceived Confirmations Report</h3>
<form method="post" action="">
<table>
    <tr>
        <td>
            <strong> {{ form.start_date.label }}</strong> {{ form.start_date }}
            <strong>{{ form.end_date.label }}</strong> {{ form.end_date }}
        </td>
    </tr>
</table>
<input type="submit" value="View Report">
    <input type="submit" name="print_report_submit" value="Print Report"/>
</form>
    {% for key, value in confirmlist.items %}
        {{ key }} - {{ value }}
    {% endfor %}
{% endblock %}

I get nothing.

Here is a sample of the output I get when testing in the views.py

33 [{'fi_address1': u'Scotiabank FAS', 'fi_country': u'Canada', 'fi_address2': u'20 Queen Street West, Suite 2600', 'fi_city': u'TORONTO', 'fi': <FinancialInstitution: NATIONAL TRUST>, 'fi_prov': u'Ontario', 'fi_postal': u'### ###', 'purchase_amount': Decimal('30000.00'), 'purchase_date': datetime.date(2011, 6, 27), 'type': u'GIC', 'sin': u'###/###/###', 'primary_owner': <Member: #, #>}]

Answer 1

This happens because of the way the Django template language does variable lookups. When you try to loop through the dictionaries items,

{% for key, value in confirmlist.items %}

Django first does a dictionary lookup for confirmlist['items']. As this is a defaultdict, an empty list is returned.

It’s a cruel gotcha, that I’ve been stung by as well!

To work around this problem, convert your defaultdict into a dictionary before adding it to the template context.

context['confirmlist'] = dict(confirm_list)

Or, as explained by sebastien trottier in his his answer to a similar question, set
default_factory to None before adding to the template context.

confirm_list.default_factory = None
context['confirmlist'] = confirm_list