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 isNone. 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'
Use the none test (not to be confused with Python's None object!):
{% if p is not none %}
{{ p.User['first_name'] }}
{% else %}
NONE
{% endif %}
or:
{{ p.User['first_name'] if p is not none else 'NONE' }}
or if you need an empty string:
{{ p.User['first_name'] if p is not none }}
none in the answer. My problem was solved after I corrected None's case.
False and None. This example uses the term "first_name" which we can assume will not expect a value of False, but there are many cases where a system needs to treat False and None differently. Things like {{p.User['first_name'] or 'default'}} will not catch that case and will convert False to the default case incorrectly. Other interesting cases are 0, [], and "".
!= None works but is not None don't and for this, you need to use in lowercase: is not none{{p.User['first_name'] or 'My default string'}}
p.User['first_name'] is false will the result be as expected: false?According to docs you can just do:
{{ p|d('', true) }}
Cause None casts to False in a boolean context.
default is exactly what I needed for my particular case, so... simply not voting. (An edit to this answer might well earn it an upvote, except that I think it's likely hard to apply default to this situation)
default only works in simple data types is outdated. I have this working with an empty list, default([])As addition to other answers, one can write something else if variable is None like this:
{{ variable or '' }}
x or y is if x is false, then y, else x. See: 5.2. Boolean Operations — and, or, not
Following this doc you can do this that way:
{{ p.User['first_name']|default('NONE') }}
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" }}
if you want to set your own default value instead of None than simply do this
{{your_var|default:'default name'}}
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.
for 0 value i need to use if val is None else structure, so added filter ifnone:
def ifnone(val, default):
if val is None:
return default
return val
...
env.filters["ifnone"] = ifnone
Useage in template: {{val|ifnone('--')}}
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>
I solved this by defining a custom filter (in my case I needed in the cases None, False or empty strings):
def __default_if_empty(value, default) :
"""Returns a default value if the given value evaluates to False."""
return value if value else default
env = Environment(
# Your config...
)
env.filters["default_if_empty"] = __default_if_empty
Then use that filter in the template:
{{ your_var | default_if_empty('') }}
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) }}
pnever returnNone. Instead ofNonethe function should return a proxy object that has the same structure as a real object but it is loaded with the default values that you want.