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

1. How can we use python in the templates?

2. Is passing a param to the template in the def get(self) method the only way to do this?

3. 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.

Solution 1

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.

Solution 2

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

i Solve it with that way!!

Solution 3

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

That should solve your problem.

You can check out this link.

Comments

[tipsywacky]

exactly what i'm looking for. thanks.

[Lava Sangeetham]

i am getting following error TypeError: count() takes exactly one argument (0 given)

[edumike]

For quick reference: {% if alist|length == 0 %}

[Henning]

-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 ;)

[Will Jenkins]

Since when was 'RTFM' considered an acceptable or helpful answer?

[Amit Pathak]

count() counts a specific item. I don't think this works, please correct if required.