Converting from Django, I'm used to doing something like this:
{% if not var1 %} {% endif %}and having it work if I didn't put var1 into the context. Jinja2 gives me an undefined error. Is there an easy way to say {% if var1 == None %} or similar?
7 Answers
From the Jinja2 template designer documentation:
{% if variable is defined %} value of variable: {{ variable }}
{% else %} variable is not defined
{% endif %}{% if variable is defined %} is true if the variable is None.
Since not is None is not allowed, that means that
{% if variable != None %}
is really your only option.
4You could also define a variable in a jinja2 template like this:
{% if step is not defined %}
{% set step = 1 %}
{% endif %}And then You can use it like this:
{% if step == 1 %}
<div>
{% elif step > 1 %}
<div>
{% else %}
<div>
{% endif %}Otherwise (if You wouldn't use {% set step = 1 %}) the upper code would throw:
UndefinedError: 'step' is undefinedIn the Environment setup, we had undefined = StrictUndefined, which prevented undefined values from being set to anything. This fixed it:
from jinja2 import Undefined
JINJA2_ENVIRONMENT_OPTIONS = { 'undefined' : Undefined }Consider using default filter if it is what you need. For example:
{% set host = jabber.host | default(default.host) -%}or use more fallback values with "hardcoded" one at the end like:
{% set connectTimeout = config.stackowerflow.connect.timeout | default(config.stackowerflow.timeout) | default(config.timeout) | default(42) -%}{% if variable is defined %} works to check if something is undefined.
You can get away with using {% if not var1 %} if you default your variables to False eg
class MainHandler(BaseHandler): def get(self): var1 = self.request.get('var1', False)I had an issue like this in Ansible. Ended up having to do a test on both @Garret and @Carsten / @azalea answers, so:
{% if variable is defined and variable %} value of variable: {{ variable }}
{% else %} variable is not defined or is falsy
{% endif %}
