Here is a version which uses epoll to service a number of pipes which is larger than maxevents.  (If NUM_WRITERS is too large then I get "OSError: [Errno 24] Too many open files".)

All pipes get serviced and the output is:

Working with 20 FDs, 5 maxevents
[5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43]
[15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43]
[25, 27, 29, 31, 33, 35, 37, 39, 41, 43]
[35, 37, 39, 41, 43]

The lists show the (sorted) unseen writers at each loop.