Question

Let’s say, I created a template object (f.e. using environment.from_string(template_path)). Is it possible to check whether given variable name exist in created template?

I would like to know, if

template.render(x="text for x")

would have any effect (if something would be actually replaced by “text for x” or not). How to check if variable x exist?

Answer 1

From the documentation:

defined(value)

Return true if the variable is defined:

{% if variable is defined %}
    value of variable: {{ variable }}
{% else %}
    variable is not defined
{% endif %}
See the default() filter for a simple way to set undefined variables.

EDIT:
It seems you want to know if a value passed in to the rendering context. In that case you can use jinja2.meta.find_undeclared_variables, which will return you a list of all variables used in the templates to be evaluated.