Python jinja2 template, how to count a list

Question

So I can't use python len() for a list in the templates like below.

{% if len(alist) == 0 %}

UndefinedError: 'len' is undefined

How can we use python in the templates?
Is passing a param to the template in the def get(self) method the only way to do this?
Anyone know some good resources on how to use jinja2 with it comes to templating? like what methods can you use and the syntactic difference between python and jinja2.

score 29 · Answer 1 · edited Aug 01 '15 at 20:53

29

{% if alist |length ==0 %}  or  {% if alist |count ==0 %}

i Solve it with that way!!

edited Aug 01 '15 at 20:53

Uli Köhler

answered May 26 '15 at 04:08

buoge

score 22 · Accepted Answer · answered Feb 05 '13 at 08:26

22

If you do a quick search in the template documentation you will quite soon find the length filter.

As for the rest, read the documentation.

answered Feb 05 '13 at 08:26

19

For quick reference: {% if alist|length == 0 %} – edumike Oct 03 '17 at 21:28
18

-1 cause you could have saved us your remark implying the person asking the question being too lazy to search the docs. Some things you dont find as easy if you don't know exactly what to search for. And IMHO it's the responsiblity of Jinja's authors to create a template language that looks like being "normal" python, but in certain corner cases isn't, and then throwing pretty unclear error messages. Thanks for the 1/4 helpful part of your answer ;) – Henning Sep 05 '19 at 19:51
5

Since when was 'RTFM' considered an acceptable or helpful answer? – Will Jenkins Oct 22 '20 at 17:46

score 1 · Answer 3 · edited May 23 '17 at 12:17

1

{% if alist.count() == 0 %}

That should solve your problem.

edited May 23 '17 at 12:17

Community

answered Jul 02 '13 at 13:54

Sunkanmi Akintoye

17

i am getting following error TypeError: count() takes exactly one argument (0 given) – Lava Sangeetham Mar 15 '17 at 17:19
`count()` counts a specific item. I don't think this works, please correct if required. – Amit Pathak Mar 26 '22 at 12:54

3 Answers3