Festival in middle of Kadiri always polite? (6)

I believe the answer is:

diwali

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'festival' is the definition.
(Hindu festival)

'middle of kadiri always polite?' is the wordplay.
'middle of' indicates the central letters.
'always polite?' becomes 'wali' (I can't explain this - if you can you should believe this answer much more).
The middle letters of 'kadiri' are 'di'.
'di'+'wali'='DIWALI'

'in' acts as a link.

Can you help me to learn more?

(Other definitions for diwali that I've seen before include "Light festival" , "Festival in honour of Lakshmi" , "religious festival" , "Indian festival" , "Hindu festival of lights" .)

I've seen this clue in The Irish Times.

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