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======
The ``if`` statement in Twig is comparable with the if statements of PHP.
In the simplest form you can use it to test if an expression evaluates to
``true``:
.. code-block:: jinja
{% if online == false %}
<p>Our website is in maintenance mode. Please, come back later.</p>
{% endif %}
You can also test if an array is not empty:
.. code-block:: jinja
{% if users %}
<ul>
{% for user in users %}
<li>{{ user.username|e }}</li>
{% endfor %}
</ul>
{% endif %}
.. note::
If you want to test if the variable is defined, use ``if users is
defined`` instead.
You can also use ``not`` to check for values that evaluate to ``false``:
.. code-block:: jinja
{% if not user.subscribed %}
<p>You are not subscribed to our mailing list.</p>
{% endif %}
For multiple conditions, ``and`` and ``or`` can be used:
.. code-block:: jinja
{% if temperature > 18 and temperature < 27 %}
<p>It's a nice day for a walk in the park.</p>
{% endif %}
For multiple branches ``elseif`` and ``else`` can be used like in PHP. You can
use more complex ``expressions`` there too:
.. code-block:: jinja
{% if kenny.sick %}
Kenny is sick.
{% elseif kenny.dead %}
You killed Kenny! You bastard!!!
{% else %}
Kenny looks okay --- so far
{% endif %}
.. note::
The rules to determine if an expression is ``true`` or ``false`` are the
same as in PHP; here are the edge cases rules:
====================== ====================
Value Boolean evaluation
====================== ====================
empty string false
numeric zero false
whitespace-only string true
empty array false
null false
non-empty array true
object true
====================== ====================
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