Built in template functions
===========================




defined(key)
------------------------

Return ``True`` if a variable named ``key`` is defined, else ``False``.


.. code:: html

    <!--
    Will only produce output if a variable 'message' has been defined
    -->
    <h1 py:if="defined('message')">$message</h1>




value_of(key, [default])
------------------------

Return the value of the variable named ``key`` if it exists, else ``default``.

.. code:: html

    <!--! Outputs 'today it is rainy' -->
    <div py:with="weather='rainy'">today it is ${value_of('weather', 'sunny')}</div>

    <!--! Outputs 'today it is sunny' -->
    <div>today it is ${value_of('weather', 'sunny')}</div>



super()
----------

Render the parent block when using template inheritance. This function is only available inside Piglet :ref:`py-block` directives.

Example:

.. code:: html

    <!-- file: layout.html -->

    <section py:block="content">
        <p>Eat more biscuits</p>
    </section>


.. code:: html

    <!-- file: index.html -->
    <py:extends href="layout.html">
        <section py:block="content">
            <p>Drink more tea</p>
            <p>${super()}</p>
        </section>
    </py:extends>

This would produce the following output:

.. code:: html

    <section>
        <p>Drink more tea</p>
        <p>Eat more biscuits</p>
    </section>