Sequential Numbering Python Script for Field Calculator in Arc 10.2

KennyDonaldson

Hi

I'm looking for a python script to populate an ID field in ACRGIS 10.2 with a sequential number that resets when the value of site field changes. e.g.

Site      ID

SIte A   0001

Site A   0002

SIte A   0003

Site A   0004

SIte A   0005

Site B   0001

SIte B   0002

Site B   0003

Site C   0001

SIte C   0002

...           .....

I've been using Arc for a number of years but have no python skills yet.

Thanks

Kenny