Django - passing an attribute value to as_view in TemplateView

Question

This is my view (simplified):

class MyView(TemplateView):
    def __init__(self):
        self.foo = 'bar'
        super(MyView, self).__init__()

This is in urls.py:

url(
    r'^/foo/$',
    MyView.as_view(foo='baz'), name='my_view'
)

When I run this, I get the following error:

TypeError: MyView() received an invalid keyword 'foo'. as_view only accepts arguments that are already attributes of the class.

Why? I thought this would work. :/

At least according to this post: http://reinout.vanrees.org/weblog/2011/08/24/class-based-views-walkthrough.html#class-view

If I understood this correctly, this should have set the attribute foo to the value 'baz' passed in as_view. Without any attributes in as_view, the value should be 'bar', as defined in __init__.

Answer 1

You're explicitly setting a value on an instance of the class in __init__(). However, the class itself still doesn't have an attribute foo, as it is unaware of dynamic attributes on instances: hasattr(MyView, 'foo') always returns False.

This would work as you expected your code to work:

class MyView(TemplateView):
    foo = 'bar'

url(
    r'^/foo/$',
    MyView.as_view(foo='baz'), name='my_view'
)

Answer 2

The source code of Django View class has this though:

if not hasattr(cls, key):
    raise TypeError

So it is not enough to create the attr on an instance in __init__ ...it has to exist on the class itself:

class MyView(TemplateView):
    foo = 'bar'