Programmers finally put in extra code (5)
I believe the answer is:
morse
'code' is the definition.
(Morse code)
'programmers finally put in extra' is the wordplay.
'finally' indicates one should take the final letters.
'put in' means one lot of letters goes inside another.
'extra' becomes 'more' (both can mean additional).
The final letter of 'programmers' is 's'.
's' put within 'more' is 'MORSE'.
(Other definitions for morse that I've seen before include "Radio code inventor" , "Dot-dash code inventor" , "Fictional inspector; code" , "Samuel ---, telegraph inventor" , "Code using dots and dashes" .)