I nip round with endless dope for festival (5,4)

I believe the answer is:

mardi gras

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'festival' is the definition.
(Mardi Gras is an example)

'i nip round with endless dope' is the wordplay.
'nip' becomes 'dram' (I've seen this in another clue).
'round' is a reversal indicator.
'with endless dope' becomes 'gras' (I can't justify this - if you can you should give a lot more credence to this answer).
'i'+'dram'='idram'
'idram' reversed gives 'mardi'.
'mardi'+'gras'='MARDI GRAS'

'for' is the link.

Can you help me to learn more?

(Other definitions for mardi gras that I've seen before include "Day for 9 acrosses" , "festive occasion" , "Revelry celebrating Shrove Tuesday" , "The lead up to fast" , "Shrove Tuesday festival" .)

I've seen this clue in The Times.

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