How to catch specific error in any template in Django? - django

Question

I want to catch custom exception that I raise in a method called from base.html. When it happens, I need to redirect user to another page. Where is the best place to do this?
Below is simplified example of code to show the problem
base.html:
{% if something %}{{ widget_provider.get_header }}{% endif %}
widget_providers.py
class SpecificWidgetProvider(BaseWidgetProvider):
def get_header(self):
if self.user.is_anonimous():
raise AuthenticationRequired()
return third_party_api.get_top_secret_header_widget()
AuthenticationRequired exception may be raised by many parts of my site (most time in views), and I want to keep the handler in one place. So I created a middleware to catch this type of exception.
middleware.py
def process_exception(request, exception):
if isinstance(exception, AuthenticationRequired):
return redirect('accounts:login')
But I've found that class based views may leave the template rendering phase for later. They just return TemplateResponse instance, and Django's request handler (get_response() in django.core.handlers.base) calls response.render() outside of all middlewares stack. So now my middleware can't catch the exception. Maybe it is better to call get_header() from context processor, but this does not help too.

Answer 1

I solved the problme by prefetching the data within try/except in process_template_response() in the same middleware, and moved error processing to common private method. This allows me to keep error processing in the same place.
def process_template_response(self, request, response)
try:
widget_provider.get_header()
except AuthenticationRequired:
response = self._process_auth_required()
# Bind render() method that just returns itself, because we must
# return TemplateResponse or similar here.
def render(self):
return self
response.render = types.MethodType(render, response)
return response
def process_exception(self, request, exception):
if isinstance(exception, AuthenticationRequired):
return self._process_auth_required()
def _process_auth_required(self):
return redirect('accounts:login')