Jinja2: Change the value of a variable inside a loop
Question:
I want to change the value of the variable declared outside the loop within a loop. But always changing, 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 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, its is very ugly! Is there another more elegant solution?
Answers:
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)
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)!
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 %}
I want to change the value of the variable declared outside the loop within a loop. But always changing, 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 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, its is very ugly! Is there another more elegant solution?
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)
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)!
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 %}