Jinja2 Exception Handling

Question

Is there a way to handle exceptions within a template in jinja2?

{% for item in items %}
   {{ item|urlencode }}  <-- item contains a unicode string that          


        

Answer 1

While jinja2 does not have a way to handle this by default, there is a workaround.

Since try is not supported in the template language, we need a helper function defined in Ppython, like this:

def handle_catch(caller, on_exception):
    try:
         return caller()
    except:
         return on_exception

This method is injected into the template engine, either via the Environment.globals or when calling the render method. In this example it is injected via the render method.

my_template.render(handle_catch=handle_catch)

In the template itself it is then possible to define a macro:

{% macro catch(on_exception) %}
    {{ handle_catch(caller, on_exception) }}
{% endmacro %}

And this can then be used as:

{% for item in items %}
   {% call catch('') %}
       {{ item | custom_urlencode_filter }}
   {% endcall %}
{% endfor %}

Notes:

• The caller method is provided by the jinja2, and this is a function that renders the code between {% call ... %} and {% endcall %}
• on_exception can be used to provide an alternative text in case of exceptions, but in this case we just use an empty string.