if
Show a block if the condition is true.
The {% if %} tag evaluates an expression and if the result is true (boolean true, number unequal to zero, non empty string or a non empty list) then the contents of the if-block are output.
If the if-test fails then the optional {% elif %} blocks are evaluated. If both the if-test and all elif-tests fail, then the {% else %} block contents are output.
Example:
{% if genre == "pop" %}
Popular music.
{% elif genre == "classical" %}
Classical music.
{% elif genre == "jazz" %}
Jazz
{% else %}
The genre isn't pop, classical or jazz.
{% endif %}
An {% if %} and {% elif %} tag can have an “and” or “or” expression as argument:
{% if person_list and show_persons and full_moon %}
There are persons that we can show during full moon.
{% endif %}
Or for example:
{% if new_moon or daytime %} Guess you can’t see the moon. {% endif %}
It is also possible to mix “and” and ”or” in one expression, so this is a valid:
{% if full_moon or daytime and cloudy %}
The evaluation order is: and, xor, and then or. Left to right associative.
So the above is equivalent to:
{% if full_moon or (daytime and cloudy) %}
The ”not” operator can be used to negate a boolean value:
{% if full_moon or daytime or not clearsky %}
if-with
The if is often combined with the with tag. For example:
{% with m.search[{latest cat=`news` pagelen=10}] as result %}
{% if result %}
<h3>{_ Latest news _}</h3>
<ul>
{% for id in result %}
<li><a href="{{ id.page_url }}">{{ id.title }}</a></li>
{% endfor %}
</ul>
{% endif %}
{% endwith %}
To make this easier it is possible to combine the if and with tags in a single expression:
{% if m.search[{latest cat=`news` pagelen=10}] as result %}
<h3>{_ Latest news _}</h3>
<ul>
{% for id in result %}
<li><a href="{{ id.page_url }}">{{ id.title }}</a></li>
{% endfor %}
</ul>
{% endif %}
The as can also be used in the elif expressions:
{% if expression1 as x %}
...
{% elif expression2 as y %}
...
{% else %}
...
{% endif %}