Opened 4 years ago

Closed 4 years ago

#32526 closed Bug (invalid)

Class based custom template filters seem to be broken since Django 2.0

Reported by: 884756834 Owned by: starryrbs
Component: Template system Version: 3.1
Severity: Normal Keywords:
Cc: Triage Stage: Unreviewed
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description (last modified by 884756834)

In Django 1.10, writing a custom template filter using a class used to work:

Code highlighting: 

class MyCustomFilter(object):
    __name__ = 'custom_filter'

    def __call__(self, value):
        if not isinstance(value, str):
            return value

        return MyHelperClass(value).do_stuff()

custom_filter = MyCustomFilter()

But in Django 2.2 (and likely from 2.0 to 3.1) this seems to raise an error:

django.template.exceptions.TemplateSyntaxError: "requires 2 arguments, 1 provided"

I believe it is caused by the changes in one of, or both, these 2 commits:

​https://github.com/django/django/commit/c2a1af883e18b93a77080650feb9e959536d51ca
​https://github.com/django/django/commit/620e9dd31a2146d70de740f96a8cb9a6db054fc7

As a workaround, I've been able to rewrite it:

Code highlighting: 

def custom_filter(value):
    if not isinstance(value, str):
        return value

    return MyHelperClass(value).do_stuff()

Change History (4)

comment:1 by 884756834, 4 years ago

Description: modified (diff)

comment:2 by 884756834, 4 years ago

Description: modified (diff)

comment:3 by starryrbs, 4 years ago

Owner: changed from nobody to starryrbs
Status: new → assigned

comment:4 by Mariusz Felisiak, 4 years ago

Resolution: → invalid
Status: assigned → closed

Class-based custom template filters have never been officially supported or tested, see ​"Writing custom template filters" docs:

"Custom filters are Python functions that take one or two arguments..."

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