One of the most common tags that you will use will be the for tag to implement for loops inside your HTML documents. The for tag allows you to navigate through a list of strings or objects and generate HTML code for each item in the list.

For example, if you have a list of several URLs for which you want to write HTML links in a template, you could implement a for tag similar to the following code snippet, where links is a list object:

{% for lnk in links %}
    <li><a href="{{ lnk }}"> {{ lnk }}</a></li>
{% endfor %}

Using this code in your template renders the list of links in the HTTP response. It doesn’t matter how many links you need to put in the list. You do not need to add code to your HTML template to do so.

The for tag can also handle dictionary objects. Use the following syntax:

{% for key, value in dict %}

For example, if you have a dictionary containing people’s names as the key and phone numbers as the value, you could use the following code snippet in a template to render the list of names and phone numbers:

{% for name, phone in phoneList %}
    <h2>Name:  {{ name }} </h2>
    <li>Phone:  {{ phone }} </li>
{% endfor %}

{% for title in books reversed %}

Django also allows you to use for loops to process lists of lists as long as you can unpack the values in each sublist into a set of names. For example, if you have a list of GPS coordinates that are formatted as a [location, lat, long] list, you could use the following code snippet in a template to render the list of GPS locations:

{% for location, lat, long in gpsList %}
    <h2>Location:  {{ location }} </h2>
    <li>Coordinates:  {{ lat }}:{{ long }}</li>
{% endfor %}

Django provides the forloop variable in loop operations. It can provide you with information such as counters and parent loops. Table 8.1 lists the available fields in the forloop variable object.

{% extends "iFriends_base.html" %}

{% block title %}People{% endblock %}
{% block content %}
<table width=100%>
<tr bgcolor="aabbcc"><td colspan="3">
<font size="5" color="white">Personal List</font>
</td></tr>
<tr valign="top"><td width=30% bgcolor="aaaaaa"><font 
color="white" size="5">
{% for p in pList %}
    <p>{{ forloop.counter }}. {{ p.name }}</p>
{% endfor %}
</font></td></tr>
{% endblock %}

from django.http import HttpResponse
from iFriends.People.models import Person
from django.shortcuts import render_to_response, get_object_or_404

def index(request):
    pList = Person.objects.all()
    return render_to_response('people/person_index.html',
 {'pList': pList})

def details(request, pID='0', opts=()):
    p = get_object_or_404(Person, pk=pID)
    return render_to_response('people/person_details.html', {'p': p})

Django also provides rudimentary if logic to the template parser. You can use the if, ifchanged, ifequal, and ifnotequal tags to determine how and if content should be displayed. The following sections describe the different types of if tags and their uses.

{% if carList %}
    {% for car in carList %}
        <li>{{ car.model }}</li>
    {% endfor %}
(% else %}
    No cars in list.
{% endif %}

{% if not carList %}
   No cars in list.
 (% else %}
     {% for car in carList %}
        <li>{{ car.model }}</li>
    {% endfor %}
{% endif %}

{% if studentList and teacherList %}
    <h2>Students</h2>
    {% for s in studentList %}
        <li>{{ student }}</li>
    {% endfor %}
    <h2>Students</h2>
    {% for s in studentList %}
        <li>{{ student }}</li>
    {% endfor %}
{% endif %}

{% for b in blogList %}
    {% ifchanged b.date.date %}
        <h2>Date: {{ b.date.date }} </h2>
    {% endifchanged %}
    <h1>{{ b.title }}</h1>
    {{ b.text }}
{% endfor %}

{% ifchanged %}<h3>{{ b.date }}</h3> {% endifchanged %}

{% for user in userList %}
    <h1>Arthurs</h1>
    {% ifequal user.last "Arthur" %}
        <li>{{ user.first }}</li>
    {% endifequal %}
{% endfor %}

{% for blog in blogList %}
    {% ifnotequal blog.title "test" %}
        <h1>{{ blog.title }}</h1>
        {{ blog.text }}
    {% endifnotequal %}
{% endfor %}

{% extends "iFriends_base.html" %}

{% block title %}Details{% endblock %}
{% block content %}
<table width=100%>
<tr bgcolor="aabbcc"><td colspan="3">
<font size="5" color="white">Personal Information</font>
</td></tr>
<tr valign="top"><td width=30% bgcolor="aaaaaa"><font 
color="white" size="5">
    <li>Name: {{p.name}}</li>
    <li>Birthday: {{ p.birthday }}</li>
    <li>Gender:
        {% ifequal p.gender "M" %}
            Bloke
        {% else %}
            Sheila
        {% endifequal %}
    </li>
    <li>Desc: {{ p.desc }} </li>
</font></td>
<td width=40% bgcolor="aa99aa"><font color="white" size="4">
    {% include "quote.html" %}
</font></td>
<td width=30%>
    <h3>Contact Info</h3>
    <li>Email: {{ p.email }}</li>
    <li>Website: {{ p.favoriteURL }}</li>
</td></tr>
{% endblock %}

Django provides the url tag to help you add links to your web pages. If possible, it is best to avoid hard-coded links. If you modify the URLconf file and thus change the URL pattern, you might wind up needing to change every place in your code that you hard-coded the link.

To solve this problem, the url tag allows you to specify the view function, including arguments, directly. The url tag results in an absolute URL being placed in the rendered HTML document.

The first argument inside the url tag is a path to a view function, such as the path to the details() function in the views.py file of the People application in the iFriends project:

iFriends.People.views.details

Additional arguments are optional and should be separated by commas with no spaces. Arguments are considered positional unless you specify a keyword=value. For example:

{url mySite.arch.views.list arg1,arg2,year=2008 %}

The arguments specified in the url tag must correspond to what is defined in the URLconf file. If they do not, no URL is returned.

{% extends "iFriends_base.html" %}

{% block title %}People{% endblock %}
{% block content %}
<table width=100%>
<tr bgcolor="aabbcc"><td colspan="3">
<font size="5" color="white">Personal List</font>
</td></tr>
<tr valign="top"><td width=30% bgcolor="aaaaaa"><font 
color="white" size="5">
{% for p in pList %}
    <li>
    <a href="{% url iFriends.People.views.details p.id %}">{{ p.
name }}</a>
    </li>
{% endfor %}
</font></td></tr>
{% endblock %}

Another template tag that you will find useful is with. The with tag allows you to assign a complex variable name a simpler one. This is most helpful when you have to reference the object several times.

For example, consider the business.accounting.contact_info subobject. Referencing that object several times would take a lot of keystrokes. The following example shows how to use the with tag to reduce the code necessary to reference the object:

{% with business.accounting.contact_info as ci %}
Phone: {{ ci.phone }}
Email: {{ ci.email }}
Website: {{ci.URL }}
{% endwith %}

The cycle tag is a useful tool if you need to modify values as you cycle through a list. The cycle tag accepts a comma-separated list of arguments that will be cycled through.

For example, if you were creating a large table in your template and you wanted each row of the template to use a different background color, you could use the cycle tag to set the bgcolor value of the rows. The following code generates the web page shown in Figure 8.5:

<table width=100%>
{% for line in report %}
    {% if forloop.first %}
    <tr bgcolor="aaaaaa">
    {% else %}
    <tr bgcolor="{% cycle eeeeee,cccccc %}">
    {% endif %}
    {% for item in line %}
        <td>{{ item }}</td>
    {% endfor %}
    </tr>
{% endfor %}
</table>

Figure 8.5. Table generated with alternating dark and light lines using the cycle tag.

In this hour, you learned how to use template tags to add logic in your templates. You learned how to generate several lines of HTML code from a list using the for tag. You also learned how to add HTML code conditionally using the if, ifchanged, ifequal, and ifnotequal tags.

Using loops, conditions, and other tags enables you to write simpler and more useable code and makes it easier to modify and update your website.

The workshop consists of a set of questions and answers designed to solidify your understanding of the material covered in this hour. Try answering the questions before looking at the answers.