Panda's Write CSV - Append vs. Write

Question

I would like to use pd.write_csv to write "filename" (with headers) if "filename" doesn't exist, otherwise to append to "filename" if it exists. If I simply use command:

     df.to_csv('filename.csv',mode = 'a',header ='column_names') 

The write or append succeeds, but it seems like the header is written every time an append takes place.

How can I only add the header if the file doesn't exist, and append without header if the file does exist?

Answer 1

Not sure there is a way in pandas but checking if the file exists would be a simple approach:

import os # if file does not exist write header  if not os.path.isfile('filename.csv'):    df.to_csv('filename.csv', header='column_names') else: # else it exists so append without writing the header    df.to_csv('filename.csv', mode='a', header=False)