>>> import datetime
>>> your_timestamp = 1331856000000
>>> date = datetime.datetime.fromtimestamp(your_timestamp / 1e3)
>>> date
datetime.datetime(2012, 3, 16, 1, 0)
# importing pandas package
import pandas as pd
#date to datetime
df['Dates'] = pd.to_datetime(df['Dates'], format='%Y%m%d')