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 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.
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
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) -%}
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' }}
Jinja templates - Template Designer Documentation
{% 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 %}
You can do this :
- debug:
msg: "Executed only if variable is defined"
when:
- variable is defined
Related
I have a use case where I would like to define the name of a macro and then apply it to one column.
A simplified example could be as follows. I have two macros defined that I want to call dynamically in my model (both take one column as an input):
cast_to_string
convert_empty_string_to_null_value
Now, I want to call them dynamically. See the example below
{%- set macro_names = ["cast_to_string", "convert_empty_string_to_null_value"] -%}
select
{% for macro_name in macro_names %}
-- this should dynamically be evaluated to `{{ cast_to_string(my_column) }}`
-- and `{{ convert_empty_string_to_null_value(my_column) }}`
{{ macro_name(my_column) }}
{% endfor %}
from my_model
However, this will throw an error saying that a string is not callable.
I also tried using {% raw %} {{ {% endraw %} to escape brackets, but that didn’t work either.
So, my question is, if there is a way to dynamically call macros in jinja/dbt?
I think it should work if you remove the quotes :
{%- set macro_names = [cast_to_string, convert_empty_string_to_null_value] -%}
So that jinja doesn't interpret it as string and you can use it as a Callable
I achieve it using this example :
{%- set macro_names = [print_lower, print_upper] -%}
{% for macro_name in macro_names %}
{{ macro_name("test") }}
{% endfor %}
and
{% macro print_lower(string) %}
{{ print(string|lower) }}
{% endmacro %}
{% macro print_upper(string) %}
{{ print(string|upper) }}
{% endmacro %}
I am beginner in computer science and trying to use python flask framework to create a webserver.
In the tutorials, I have seen the below jinja usage in the HTML which are
{% set a = somefunction() %}
{% with a = somefunction() %}
May I know what are the differences? Thanks.
While you may use {% set %} to define a variable, the {% with %} statement additionally creates a new scope which can be ended using the {% endwith %} statement.
For example:
{% with myvar=1 %}
...
{% endwith %}
myvar will only be available before the corresponding endwith.
You can also use with to create a local scope:
{% with %}
{% set myvar=1 %}
...
{% endwith %}
myvar will only be available within the given scope.
You can find information about these statements here (the examples shown here were taken from there also).
Variables inside a {% with %} statement are restricted to that particular statement, while variables created via {% set %} are accessible from anywhere in the template (they are global).
>>> import jinja2
>>> t = jinja2.Template("{% set a = 'Global' %}{% with a = 'Local' %}{{ 'First a is ' + a +'\n' }}{% endwith %}{{ 'Second a is ' + a }}")
>>> print(t.render())
First a is Local
Second a is Global
Say I have two templates:
main.j2
{% include "vars.j2" %}
main: {{ var1 }}
vars.j2
{% set var1 = 123 %}
vars: {{ var1 }}
When run, only this line is output:
vars: 123
i.e. var1 is undefined in main.j2, even though it gets set to a value in the included vars.j2 template.
How can I pass variables from included template back to template that includes it? I considered chaining extends, but wondered if there's a more elegant approach.
I recently had a need to do the same thing, and found 2 solutions.
If you have Jinja version 2.10 or later, namespaces can be used:
main_ns.j2:
{% set ns = namespace() %}
{% include "vars_ns.j2" %}
main_ns: {{ ns.var1 }}
vars_ns.j2:
{% set ns.var1 = 123 %}
vars_ns: {{ ns.var1 }}
In Jinja 2.2 or later, it can be accomplished with block scoping of variables. I put the variable settings in the base template so that multiple children can extend it.
vars_block.j2:
{% set var1 = 123 %}
vars_block: {{ var1 }}
{% block content scoped %}{% endblock %}
main_block.j2:
{% extends "vars_block.j2" %}
{% block content %}
main_block: {{ var1 }}
{% endblock %}
You can try using with:
{% with var1=0 %}
{% include "vars.j2" %}
vars: {{ var1 }}
{% endwith %}
When calling items from an array in a Liquid template, how do you call does not contain or not in array?
unless to the rescue !
Create an [A, B, C] array.
{% assign input = "A,B,C" | split:"," %}
unless print only if constrain is not met.
This prints nothing:
{% unless input contains 'A' %}No A{% endunless %}
This prints "No Z":
{% unless input contains 'Z' %}No Z{% endunless %}
you could do something like this:
{% if collection.tags contains 'tag' %}
{% else %}
do stuff!
{% endif %}
I want to have one parent template and many children templates with their own variables that they pass to the parent, like so:
parent.html:
{% block variables %}
{% endblock %}
{% if bool_var %}
{{ option_a }}
{% else %}
{{ option_b }}
{% endif %}
child.html:
{% extends "parent.html" %}
{% block variables %}
{% set bool_var = True %}
{% set option_a = 'Text specific to this child template' %}
{% set option_b = 'More text specific to this child template' %}
{% endblock %}
But the variables end up undefined in the parent.
Ah. Apparently they won't be defined when they are passed through blocks. The solution is to just remove the block tags and set it up like so:
parent.html:
{% if bool_var %}
{{ option_a }}
{% else %}
{{ option_b }}
{% endif %}
child.html:
{% extends "parent.html" %}
{% set bool_var = True %}
{% set option_a = 'Text specific to this child template' %}
{% set option_b = 'More text specific to this child template' %}
If Nathron's solution does not fix your problem, you can use a function in combination with a global python variable to pass a variable value.
Advantage: The variable's value will available in all templates. You can set the variable inside a block.
Disadvantage: More overhead.
This is what I did:
child.j2:
{{ set_my_var('new var value') }}
base.j2
{% set my_var = get_my_var() %}
python code
my_var = ''
def set_my_var(value):
global my_var
my_var = value
return '' # a function returning nothing will print a "none"
def get_my_var():
global my_var
return my_var
# make functions available inside jinja2
config = { 'set_my_var': set_my_var,
'get_my_var': get_my_var,
...
}
template = env.get_template('base.j2')
generated_code = template.render(config)
In some cases, you can avoid this 'parameter-passing' by creating another variant of the parent that adds/removes some block and extends it instead.
{% extends [condition]|yesno:'parent_1.html,parent_2.html' %}