Here’s how to send redirects and HTTP errors in Pyramid compared to Pylons:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
# Pylons -- in controller action from pylons.controllers.util import abort, redirect abort(404) # Not Found abort(403) # Forbidden abort(400) # Bad request; e.g., invalid query parameter abort(500) # Internal server error redirect(url("section1")) # Redirect (default 302 Found) # Pyramid -- in view code import pyramid.httpexceptions as exc raise exc.exception_response(400) # Not Found raise exc.HTTPNotFound() # Same thing return exc.HTTPNotFound() # Same thing raise exc.HTTPForbidden() raise exc.HTTPBadRequest() raise exc.HTTPInternalServerError() raise exc.HTTPFound(request.route_url("section1")) # Redirect
The pyramid.httpexceptions module has classes for all official HTTP statuses. These classes inherit from both Response and Exception, so you can either return them or raise them. Raising HTTP exceptions can make your code structurally more readable. It’s particularly useful in subroutines where it can cut through several calling stack frames that would otherwise each need an if to pass the error condition through.
Here are the most popular HTTP exceptions:
|HTTPMovedPermanently||301||Y||Permanent redirect; client should change bookmarks.|
|HTTPFound||302||Y||Temporary redirect. |
|HTTPSeeOther||303||Y||Temporary redirect; client should use GET. |
|HTTPTemporaryRedirect||307||Y||Temporary redirect. |
|HTTPClientError||400||N||General user error; e.g., invalid query param.|
|HTTPUnauthorized||401||N||User must authenticate.|
|HTTPForbidden||403||N||Authorization failure, or general refusal.|
|HTTPNotFound||404||N||The URL is not recognized.|
|HTTPGone||410||N||The resource formerly at this URL is permanently gone; client should delete bookmarks.|
|HTTPInternalServerError||500||N||The server could not process the request due to an internal error.|
The constructor args for classes with a “Y” in the location column are (location="", detail=None, headers=None, comment=None, ...). Otherwise the constructor args are (detail=None, headers=None, comment=None, ...).
The location argument is optional at the Python level, but the HTTP spec requires a location that’s an absolute URL, so it’s effectively required.
The detail argument may be a plain-text string which will be incorporated into the error screen. headers may be a list of HTTP headers (name-value tuples) to add to the response. comment may be a plain-text string which is not shown to the user. (XXX Is it logged?)
You can register an exception view for any exception class, although it’s most commonly used with HTTPNotFound or HTTPForbidden. Here’s an example of an exception view with a custom exception, borrowed from the Pyramid manual:
1 2 3 4 5 6 7 8 9 10 11 12 13
from pyramid.response import Response class ValidationFailure(Exception): pass @view_config(context=ValidationFailure) def failed_validation(exc, request): # If the view has two formal arguments, the first is the context. # The context is always available as ``request.context`` too. msg = exc.args if exc.args else "" response = Response('Failed validation: %s' % msg) response.status_int = 500 return response
For convenience, Pyramid has special decorators and configurator methods to register a “Not Found” view or a “Forbidden” view. @notfound_view_config and @forbidden_view_config (defined in pyramid.view) takes care of the context argument for you.
Additionally, @notfound_view_config accepts an append_slash argument, which can be used to enforce a trailing-slash convention. If your site defines all its routes to end in a slash and you set append_slash=True, then when a slashless request doesn’t match any route, Pyramid try again with a slash appended to the request URL. If that matches a route, Pyramid will issue a redirect to it. This is useful only for sites that prefer a trailing slash (“/dir/” and “/dir/a/”). Other sites prefer not to have a trailing slash (“/dir” and “/dir/a”), and there are no special features for this.