Suppress "None" output as string in Jinja2

Question

How do I persuade Jinja2 to not print "None" when the value is None?

I have a number of entries in a dictionary and I would like to output everything in a single loop instead of having special cases for different keywords. If I have a value of None (the NoneType not the string) then the string "None" is inserted into the template rendering results.

Trying to suppress it using {{ value or '' }} works too well as it will replace the numeric value zero as well.

Do I need to filter the dictionary before passing it to Jinja2 for rendering?

Is there any way to do it without interfering with the template? — lajarre, Apr 14 '15 at 15:41

score 75 · Accepted Answer · edited Nov 15 '18 at 08:34

75

In new versions of Jinja2 (2.9+):

{{ value if value }}

In older versions of Jinja2 (prior to 2.9):

{{ value if value is not none }} works great.

if this raises an error about not having an else try using an else ..

{{ value if value is not none else '' }}

edited Nov 15 '18 at 08:34

zor-el

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answered Jun 21 '12 at 21:01

Joran Beasley

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1

I got an error with this: `UndefinedError: the inline if-expression evaluated to false and no else section was defined.` – Richard de Wit Jun 10 '14 at 11:26
4

`{{ value if value != None else '' }}` may be necessary to avoid the problem @GeenHenk had – robo Apr 14 '15 at 20:12
4

I think `is not None` instead of `!= None` should be used. – warvariuc Aug 05 '15 at 06:04
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Today this just gives me `TemplateAssertionError: no test named 'None'` – Kylotan Mar 20 '16 at 18:35
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As of 2017 (Jinja 2.9), you just need `{{ value if value }}`. No need of comparing to None. – cjlallana Oct 23 '17 at 12:00

score 36 · Answer 2 · answered Jul 15 '13 at 19:10

36

Another option is to use the finalize hook on the environment:

>>> import jinja2
>>> e = jinja2.Environment()
>>> e.from_string("{{ this }} / {{ that }}").render(this=0, that=None)
u'0 / None'

but:

>>> def my_finalize(thing):
...     return thing if thing is not None else ''
...
>>> e = jinja2.Environment(finalize=my_finalize)
>>> e.from_string("{{ this }} / {{ that }}").render(this=0, that=None)
u'0 / '

answered Jul 15 '13 at 19:10

SingleNegationElimination

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I think this is the smartest way to do it. However, when I tried this method with FastAPI's jinja2, `url_for()` in the template stopped working. For your information. – mitsu Dec 22 '21 at 04:28

score 29 · Answer 3 · edited Oct 26 '22 at 06:30

29

Default filter:

{{ value|default("", True) }}

edited Oct 26 '22 at 06:30

Mads Skjern

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answered Jun 21 '12 at 21:35

solarc

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this has the same problem as OP's main solution... I think this would work as {{ value|default("", **True** ) }} – Joran Beasley Jun 21 '12 at 21:39
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Without the True, this doesn't work at all. With the True, it replaces the None and the numeric zero .. so no good. – Spaceghost Jun 21 '12 at 21:42
You are right, it only works when the variable isn't defined instead of assigning None to it. But writing a filter for the None case would be worth it just for being less verbose than the chosen answer. – solarc Jun 21 '12 at 23:07
1

I like this solution the best. – corvid Aug 12 '14 at 01:08

AlexVhr · Answer 4 · 2020-11-13T01:09:09.073

23

A custom filter can solve the problem. Declare it like this:

def filter_suppress_none(val):
    if not val is None:
        return val
    else:
        return ''

Install it like this:

templating_environment.filters['sn'] = filter_suppress_none

Use it like this:

{{value|sn}}

edited Nov 13 '20 at 01:09

answered Mar 29 '14 at 09:39

AlexVhr

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Possibly the most elegant solution here. Jinja could have a filter like this, maybe with less cryptic name than "sn" :) – Peter Lada Jul 02 '14 at 03:27
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Great answer. One nitpick: `if val is not None` would be more readable. – MarredCheese Mar 29 '17 at 23:26
Also love this answer, but minor correction: 'suppress' is spelled wrong in function def. – skelliam Sep 09 '20 at 14:10

Brownbay · Answer 5 · 2014-10-24T03:09:02.090

22

According to this post from the Pocco Mailing List: https://groups.google.com/d/msg/pocoo-libs/SQ9ubo_Kamw/TadIdab9eN8J

Armin Ronacher (creater of Jinja2/Flask, etc...) recommends the following "pythonic" snippet:

{{ variable or 0 }} {{ variable or '' }}

The notion here being that once again, explicit is preferable to implicit.

Edit: The selected answer is definitely the correct one. I haven't really come across a situation where a template variable would be either a string or the numeric zero, so the above snippets might help reduce the code noise in the template.

edited Oct 24 '14 at 03:09

answered Oct 23 '14 at 20:35

Brownbay

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It was noted in the question that this does not help because it also suppresses numeric zero – Spaceghost Oct 23 '14 at 21:34

Suppress "None" output as string in Jinja2

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