@dennix sounds like you're going to be stuck with hacky workarounds, unless "show log" accepts flags to say "please don't page the output" or the like.

i've not used telnetlib, but if you can accept it taking a while, you could use either read_until or expect and look for the device's prompt. if it times out, send whichever key the device uses to fetch another page, and call read_until/expect again.