[jinja2] Jinja2 template variable if None Object set a default value

How to make a variable in jijna2 default to "" if object is None instead of doing something like this?

      {% if p %}   
        {{ p.User['first_name']}}
      {% else %}
        NONE
      {%endif %}

So if object p is None I want to default the values of p (first_name and last_name) to "". Basically

nvl(p.User[first_name'], "")

Error receiving:

Error:  jinja2.exceptions.UndefinedError
    UndefinedError: 'None' has no attribute 'User'

Following this doc you can do this that way:

{{ p.User['first_name']|default('NONE') }}

I usually define an nvl function, and put it in globals and filters.

def nvl(*args):
    for item in args:
        if item is not None:
            return item
    return None

app.jinja_env.globals['nvl'] = nvl
app.jinja_env.filters['nvl'] = nvl

Usage in a template:

<span>Welcome {{ nvl(person.nick, person.name, 'Anonymous') }}<span>

// or 

<span>Welcome {{ person.nick | nvl(person.name, 'Anonymous') }}<span>

As addition to other answers, one can write something else if variable is None like this:

{{ variable or '' }}

As of Ansible 2.8, you can just use:

{{ p.User['first_name'] }}

See https://docs.ansible.com/ansible/latest/porting_guides/porting_guide_2.8.html#jinja-undefined-values

You can simply add "default none" to your variable as the form below mentioned:

{{ your_var | default('NONE', boolean=true) }}

According to docs you can just do:

{{ p|default('', true) }}

Cause None casts to False in boolean context.

Update: As lindes mentioned, it works only for simple data types.

As another solution (kind of similar to some previous ones):

{{ ( p is defined and p.User is defined and p.User['first_name'] ) |default("NONE", True) }}

Note the last variable (p.User['first_name']) does not have the if defined test after it.

To avoid throw a exception while "p" or "p.User" is None, you can use:

{{ (p and p.User and p.User['first_name']) or "default_value" }}

{{p.User['first_name'] or 'My default string'}}