CODEWITHSUNDEEP
pythonjinja2
Shankar Cabus
Shankar Cabus

Reputation: 9792

Change the value of a variable inside a loop

I want to change the value of the variable declared outside the loop within a loop. But, even when changing hit inside the loop, it keeps the initial value outside the loop.

{% set foo = False %}

{% for item in items %}
  {% set foo = True %}
  {% if foo %} Ok(1)! {% endif %}
{% endfor %}

{% if foo %} Ok(2)! {% endif %}

This renders:

Ok(1)!

So the only (bad) solution I have found so far was this:

{% set foo = [] %}

{% for item in items %}
  {% if foo.append(True) %} {% endif %}
  {% if foo %} Ok(1)! {% endif %}
{% endfor %}

{% if foo %} Ok(2)! {% endif %}

This renders:

Ok(1)!
Ok(2)!

But, it's is very ugly! Is there another more elegant solution?

Upvotes: 131

Views: 123306

Answers (4)

Muhammad Ali khalid
Muhammad Ali khalid

Reputation: 1

I got stuck on this too, till I realized the problem and yes the solution is ugly. I'm guessing you're using flask and python. More elegant solution I came up with was to instead do those operations on variable in python instead of there and then just pass the final value through render_template. Hope it helps.

Upvotes: 0

Omer
Omer

Reputation: 1370

As mentioned in the documentation:

Please note that assignments in loops will be cleared at the end of the iteration and cannot outlive the loop scope.

but as of version 2.10 you can use namespaces:

{% set ns = namespace(foo=false) %}      
{% for item in items %}
  {% set ns.foo = True %}
  {% if ns.foo %} Ok(1)! {% endif %}
{% endfor %}

{% if ns.foo %} Ok(2)! {% endif %}

Upvotes: 112

Pashka
Pashka

Reputation: 1446

Try also dictionary-based approach. It seems to be less ugly.

{% set vars = {'foo': False} %}

{% for item in items %}
  {% if vars.update({'foo': True}) %} {% endif %}
  {% if vars.foo %} Ok(1)! {% endif %}
{% endfor %}

{% if vars.foo %} Ok(2)! {% endif %}

This also renders:

Ok(1)!
Ok(2)!

Upvotes: 104

Daniel F
Daniel F

Reputation: 14229

You could do this to clean up the template code

{% for item in items %}
  {{ set_foo_is_true(local_vars) }}
  {% if local_vars.foo %} Ok(1)! {% endif %}
{% endfor %}
{% if local_vars.foo %} Ok(2)! {% endif %}

And in the server code use

items = ['item1', 'item2', 'item3']
#---------------------------------------------
local_vars = { 'foo': False }
def set_foo_is_true(local_vars):
  local_vars['foo'] = True
  return ''
env.globals['set_foo_is_true'] = set_foo_is_true    
#---------------------------------------------
return env.get_template('template.html').render(items=items, local_vars=local_vars)

This could be generalized to the following

{{ set_local_var(local_vars, "foo", False) }}
{% for item in items %}
  {{ set_local_var(local_vars, "foo", True) }}
  {% if local_vars.foo %} Ok(1)! {% endif %}
{% endfor %}
{% if local_vars.foo %} Ok(2)! {% endif %}

And in the server code use

items = ['item1', 'item2', 'item3']
#---------------------------------------------
local_vars = { 'foo': False }
def set_local_var(local_vars, name, value):
  local_vars[name] = value
  return ''
env.globals['set_local_var'] = set_local_var
#---------------------------------------------
return env.get_template('template.html').render(items=items, local_vars=local_vars)

Upvotes: 0

Related Questions