#30197: Template variable resolution with class objects
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Reporter: Alex Epshteyn | Owner: nobody
Type: New feature | Status: closed
Component: Template system | Version: master
Severity: Normal | Resolution: duplicate
Keywords: template, variable, | Triage Stage:
resolve | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Alex Epshteyn):
Replying to [comment:1 Tim Graham]:
> Could you detail your use case a little more? What's `Foo.Bar` some
nested class? Also, the discussion of `<type 'basestring'>` is outdated
since basestring is removed in Python 3. If you can present a patch with a
test, we can take a look, although I'm not sure it'll be backwards
compatible. I guess a documentation change may be needed to describe the
new behavior.
"Foo.Bar" is just a label used in the example template -- it could be
anything, really (I'll update the example to avoid this confusion). The
actual class is not known until run-time (otherwise we wouldn't need to
use our `type_name` filter in the first place :)). Let's just say that
`foo` is some arbitrary object that has an attribute named "bar", whose
value is a class.
In my particular use case, the code is running on the Python 2.7 runtime
of [https://cloud.google.com/appengine/docs/python/ Google App Engine] and
`foo` is an instance of
[https://cloud.google.com/appengine/docs/standard/python/refdocs/google.appengine.ext.db#google.appengine.ext.db.Property
google.appengine.ext.db.Property], and `bar` is its "data_type" attribute
(whose value is the Python class representing this datastore property's
storage type). My template is listing all the properties defined for a
particular datastore model class, including their storage type and other
metadata. For many subclasses of `db.Property`, the `data_type` is
`basestring`, but that's not really the point -- this template wouldn't
work regardless of the data type and regardless of whether it's running on
Python 2 or 3, because de-referencing this variable in a template returns
a new instance of the data type rather than the data type itself.
--
Ticket URL: <https://code.djangoproject.com/ticket/30197#comment:3>
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