Catch-All global exception handler in App Engine for Python-Collection of common programming errors

Yes it is possible.
You can do it using the ereporter package that allows to receive exception reports from your application by email.

Ereporter will report two kind of exceptions:

• exceptions logged with logging.exception('Your handled exception')
• any uncaught exceptions

To catch all the exceptions, I would create a custom BaseHandler class overriding the handle_exception() method; all your request handlers should inherit from this Base class.
Have a look to Custom Error Responses too.

Here is a simple example of BaseHandler class:

class BaseHandler(webapp.RequestHandler):

    def handle_exception(self, exception, debug_mode):
        if debug_mode:
            webapp.RequestHandler.handle_exception(self, exception, debug_mode)
        else:
            logging.exception(exception)
            self.error(500)
            self.response.out.write(template.render('templdir/error.html', {}))