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 co

Answer 1

with open(filename, 'a') as f:
    df.to_csv(f, mode='a', header=f.tell()==0)

it will add header when writes to the file first time

Answer 2

In Pandas dataframe "to_csv" function, use header=False if csv file exists & append to existing file.

    import os

    hdr = False  if os.path.isfile('filename.csv') else True
    df.to_csv('filename.csv', mode='a', header=hdr)

Answer 3

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)