One who mesmerises pythons, it turns out (9)
I believe the answer is:
hypnotist
'one who mesmerises' is the definition.
(I've seen this before)
'pythons it turns out' is the wordplay.
'turns out' indicates an anagram.
'pythons'+'it'='pythonsit'
'pythonsit' with letters rearranged gives 'HYPNOTIST'.
(Other definitions for hypnotist that I've seen before include "stage entertainer" , "Mesmeriser" , "charmer" , "One who mesmerises" , "Mesmerising person" .)