Hi Snigdha, Pondicherry best visit months are from October to March! On season here is December month - Christmas time but very much crowded and costly. Rest of the months it's pretty good to travel with less budget and less crowd. If you would like to know more please follow my Mini goa blog on Tripto.
You can visit Pondicherry during the months of October to March as the temperature usually ranges between 15 - 30 degree celcius. Over the years, Pondicherry has truly been the gem of South India and an ideal vacation spot. Summers (April-June) are quite hot and the temperature touches 40 degree Celsius occasionally.