Change time format using pandas

Question

I have a column with time format as ie 1200, how could I change in that format 12:00:00 ?

df['start_time'] = pd.to_datetime(df.start_time, format='%H:%M:%S')

Using the above I took the following error
ValueError: time data u'1200' does not match format '%H:%M' (match)

Any ideas?

Answer 1

Use to_datetime with strftime:

df['start_time'] = pd.to_datetime(df.start_time, format='%H%M').dt.strftime('%H:%M:%S')