Tornado: How to send default file if not found in StaticFileHandler

Question

When a requested static file is not found, I want to send back a default file. eg. /images/dog.png -> /images/default.png.

After digging into the source code here.

if (os.path.isdir(absolute_path) and
    self.default_filename is not None):

Setting default_filename is used for request like /images/ -> /images/default.png.

Answer 1

Interesting validate_absolute_path function, why not override this to provide your default file if not exist ?

import tornado 
import tornado.web
import tornado.ioloop

import os

DEFAULT_ABSPATH = os.path.dirname(os.path.abspath(__file__))

class StaticFileOrDefaultHandler(tornado.web.StaticFileHandler):

    def validate_absolute_path(self, root, absolute_path):
        try:
            return super(StaticFileOrDefaultHandler, self).validate_absolute_path(root, absolute_path)
        except tornado.web.HTTPError as e:
            if e.status_code == 404:
                return os.path.join(DEFAULT_ABSPATH, 'default.png')
            raise e


app = tornado.web.Application([
    (r'/(.*)', StaticFileOrDefaultHandler, { 'path': DEFAULT_ABSPATH }),
])

if __name__ == '__main__':
    app.listen(8888)
    tornado.ioloop.IOLoop.instance().start()

edit

To avoid override HTTPError(403) check with the status_code if the raised error is a 404.