from django.template import RequestContext

class PropertyBasedContext(RequestContext):
    """
    This approach allows you to avoid code duplication to 
    produce same context data for different views. 
    
    It could be usefull when you are using templates inheritace.

    EXAMPLE:

    # views.py

    class CommonContext(PropertyBasedContext):
        def _get_common(self):
            return self.request.session.get('common')
        common = property(_get_common)

    class SomeContext(CommonContext):
        def _get_some(self):
            return "My first snippet"
        some = property(_get_some)

    class OtherContext(CommonContext):
        def _get_other(self):
            return MyModel.objects.all()
        other = property(_get_other)

    def some_view(request):
        return render_to_response('some_template.html',
                              my_data_dictionary,
                              context_instance=SomeContext(request))

    def other_view(request):
        return render_to_response('other_template.html',
                              my_data_dictionary,
                              context_instance=OtherContext(request))

    # base_template.html
    
    ... {{common}} ...

    # some_template.html
    
    {% extends "base_template.html" %}
    ... {{some}} ...

    # other_template.html

    {% extends "base_template.html" %}
    ... {{other}} ...

    """
    def __init__(self, request, data=None, processors=None, current_app=None, use_l10n=None):

        RequestContext.__init__(
            self, request, data, processors, current_app, use_l10n)

        self.request = request

        classes, values = self.__base_classes(), { }

        for item in reversed(classes):
            for name, value in item.__dict__.items():
                if type(value) is property:
                    values[name] = value.fget(self)

        self.update(values)

    def __base_classes(self, current=None, classes=None):
        current, classes = current or self.__class__, classes or None
        classes.append(current)
        for base in current.__bases__:
            self.__base_classes(base, classes)
        return classes