Nifty/Banknifty Options weekly expiry symbol names

ramatius

Hi,
What is the naming convention for the weekly expiry symbols for Nifty & Banknifty? There seems to be two ways,

For 12Dec19 expiry, the symbol looks like NIFTY19D1212100CE .

But for 20Jan10 expiry, the symbol looks like NIFTY2010212100CE .

How do we decide between "D" and "1"?

Is there a webpage where the naming convention is specified?

Appreciate a quick answer.

Regards,
Ramakrishnan S
quantindia.in

ramatius

Ok, found the answer here