Python finally slithering by fence (6)
I believe the answer is:
paling
'fence' is the definition.
(I know that paling is a type of fence)
'python finally slithering by' is the wordplay.
'python' becomes 'Palin' (Monty Python member Michael Palin).
'finally' suggests the final letters.
'by' says to put letters next to each other.
The last letter of 'slithering' is 'g'.
'palin'+'g'='PALING'
(Other definitions for paling that I've seen before include "Barrier of stakes" , "Fence made of stakes" , "Fence post - turning white" , "is becoming whiter" .)