In http.server and SimpleHTTPRequestHandler - the send_head function is hard-coded to treat index.html and index.htm as files to return in a directory - if neither of those files are present, it lists the directory. 

It would be very nice to be able to specify other files to use as a directory index, similar to the DirectoryIndex directive from Apache.

I think it'd be straight forward to add some kind of list you could set, just like you can modify extensions_map to include other types of MIME types. 

Would it be OK to just add a directory_index list with index.html and index.htm on by default that people could do like
Handler.directory_index.append("index.htmlx") in their setup? Or would such an API be better with some kind of helper?