#35735: For python 3.10+ class property may not be accessible by Django's
template
system
---------------------------------+----------------------------------------
Reporter: Fabian Braun | Owner: Fabian Braun
Type: Uncategorized | Status: assigned
Component: Template system | Version: 5.0
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by Fabian Braun):
* owner: (none) => Fabian Braun
* status: new => assigned
Old description:
> Prior to python 3.10 class properties were always available through the
> template system. If you had a class
> {{{
> class MyClass:
> in_template = True
> }}}
> you could access the class property in the template through {{
> context_value.in_template }}.
>
> The template system first checks if the class is subscriptable (i.e.
> tries context_value["in_template"]), will fail with that and then will
> get the in_template property.
>
> As of Python 3.10 some classes actually are subscriptable and trying to
> get the item will not fail: Typing shortcuts introduced syntax like
> `list[int]`. This effectively hides class properties from the template
> system.
>
> Here's a test (that might go into
> tests/template_tests/syntax_tests/tests_basic.py) which passes on Python
> 3.9 and fails on Python 3.10+:
> {{{
> @setup({"basic-syntax19b": "{{ dict.klass.in_template }}"})
> def test_access_class_property(self):
> class MyClass(list):
> in_template = True
>
> def __init__(self, non_trivial_init):
> # This prevents the template system from turning the
> class into an instance
> return super().__init__()
>
> output = self.engine.render_to_string("basic-syntax19b", {"dict":
> dict(klass=MyClass)})
> self.assertEqual(output, "True")
>
> }}}
>
> I'd be happy to propose a fix.
New description:
Prior to python 3.10 class properties were always available through the
template system. If you had a class
{{{
class MyClass:
in_template = True
}}}
you could access the class property in the template through {{
context_value.in_template }}.
The template system first checks if the class is subscriptable (i.e. tries
context_value["in_template"]), will fail with that and then will get the
in_template property.
As of Python 3.10 some classes actually are subscriptable and trying to
get the item will not fail: Typing shortcuts introduced syntax like
`list[int]`. This effectively hides class properties from the template
system.
Here's a test (that might go into
tests/template_tests/syntax_tests/tests_basic.py) which passes on Python
3.9 and fails on Python 3.10+:
{{{
@setup({"basic-syntax19b": "{{ klass.in_template }}"})
def test_access_class_property(self):
class MyClass(list):
in_template = True
def __init__(self, non_trivial_init):
# This prevents the template system from turning the class
into an instance
return super().__init__()
output = self.engine.render_to_string("basic-syntax19b", {"klass":
MyClass})
self.assertEqual(output, "True")
}}}
I'd be happy to propose a fix.
Thanks to [https://github.com/benzkji Ben Stähli] and [https://github.com
/last-partizan Serhii Tereshchenko] for figuring out this issue.
References:
* https://github.com/django-cms/django-cms/issues/7948
--
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Ticket URL: <https://code.djangoproject.com/ticket/35735#comment:1>
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