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?
From the Jinja2 template designer documentation:
{% if variable is defined %} value of variable: {{ variable }} {% else %} variable is not defined {% endif %} 
{% if variable is not defined %} to test the inverse.
{% if variable is defined and variable %} would also check for emptiness
test: ~ and your solution could recognise that. THANK YOU :){% 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.
variable is always evaluated to True when not None, {% if variable != None %} is equivalent to {% if variable %}.
None use lowercase none {% if variable is not none %}
none.You 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 class="col-xs-3 bs-wizard-step active"> {% elif step > 1 %} <div class="col-xs-3 bs-wizard-step complete"> {% else %} <div class="col-xs-3 bs-wizard-step disabled"> {% endif %} Otherwise (if You wouldn't use {% set step = 1 %}) the upper code would throw:
UndefinedError: 'step' is undefined You can use kind of Jinja Elvis operator
{{ 'OK' if variable is defined else 'N/A' }} or additionally check emptiness
{{ 'OK' if (variable is defined and variable) else 'N/A' }} 
In 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) -%} 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 %} {% 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) 