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``for``
=======
Loop over each item in a sequence. For example, to display a list of users
provided in a variable called ``users``:
.. code-block:: jinja
<h1>Members</h1>
<ul>
{% for user in users %}
<li>{{ user.username|e }}</li>
{% endfor %}
</ul>
.. note::
A sequence can be either an array or an object implementing the
``Traversable`` interface.
If you do need to iterate over a sequence of numbers, you can use the ``..``
operator:
.. code-block:: jinja
{% for i in 0..10 %}
* {{ i }}
{% endfor %}
The above snippet of code would print all numbers from 0 to 10.
It can be also useful with letters:
.. code-block:: jinja
{% for letter in 'a'..'z' %}
* {{ letter }}
{% endfor %}
The ``..`` operator can take any expression at both sides:
.. code-block:: jinja
{% for letter in 'a'|upper..'z'|upper %}
* {{ letter }}
{% endfor %}
.. tip:
If you need a step different from 1, you can use the ``range`` function
instead.
The `loop` variable
-------------------
Inside of a ``for`` loop block you can access some special variables:
===================== =============================================================
Variable Description
===================== =============================================================
``loop.index`` The current iteration of the loop. (1 indexed)
``loop.index0`` The current iteration of the loop. (0 indexed)
``loop.revindex`` The number of iterations from the end of the loop (1 indexed)
``loop.revindex0`` The number of iterations from the end of the loop (0 indexed)
``loop.first`` True if first iteration
``loop.last`` True if last iteration
``loop.length`` The number of items in the sequence
``loop.parent`` The parent context
===================== =============================================================
.. code-block:: jinja
{% for user in users %}
{{ loop.index }} - {{ user.username }}
{% endfor %}
.. note::
The ``loop.length``, ``loop.revindex``, ``loop.revindex0``, and
``loop.last`` variables are only available for PHP arrays, or objects that
implement the ``Countable`` interface. They are also not available when
looping with a condition.
.. versionadded:: 1.2
The ``if`` modifier support has been added in Twig 1.2.
Adding a condition
------------------
Unlike in PHP, it's not possible to ``break`` or ``continue`` in a loop. You
can however filter the sequence during iteration which allows you to skip
items. The following example skips all the users which are not active:
.. code-block:: jinja
<ul>
{% for user in users if user.active %}
<li>{{ user.username|e }}</li>
{% endfor %}
</ul>
The advantage is that the special loop variable will count correctly thus not
counting the users not iterated over. Keep in mind that properties like
``loop.last`` will not be defined when using loop conditions.
.. note::
Using the ``loop`` variable within the condition is not recommended as it
will probably not be doing what you expect it to. For instance, adding a
condition like ``loop.index > 4`` won't work as the index is only
incremented when the condition is true (so the condition will never
match).
The `else` Clause
-----------------
If no iteration took place because the sequence was empty, you can render a
replacement block by using ``else``:
.. code-block:: jinja
<ul>
{% for user in users %}
<li>{{ user.username|e }}</li>
{% else %}
<li><em>no user found</em></li>
{% endfor %}
</ul>
Iterating over Keys
-------------------
By default, a loop iterates over the values of the sequence. You can iterate
on keys by using the ``keys`` filter:
.. code-block:: jinja
<h1>Members</h1>
<ul>
{% for key in users|keys %}
<li>{{ key }}</li>
{% endfor %}
</ul>
Iterating over Keys and Values
------------------------------
You can also access both keys and values:
.. code-block:: jinja
<h1>Members</h1>
<ul>
{% for key, user in users %}
<li>{{ key }}: {{ user.username|e }}</li>
{% endfor %}
</ul>
Iterating over a Subset
-----------------------
You might want to iterate over a subset of values. This can be achieved using
the :doc:`slice <../filters/slice>` filter:
.. code-block:: jinja
<h1>Top Ten Members</h1>
<ul>
{% for user in users|slice(0, 10) %}
<li>{{ user.username|e }}</li>
{% endfor %}
</ul>
|
