You can append usingto_csv by passing a file which isopen in append mode:

with open(file_name, 'a') as f:    df.to_csv(f, header=False)

Useheader=None, so as not to append the column names.

In fact, pandas has a wrapper to do this into_csv using themode argument (see Joe's answer):

df.to_csv(f, mode='a', header=False)

You can also pass the file mode as an argument to theto_csv method

df.to_csv(file_name, header=False, mode = 'a')

A little helper function I use (based on Joe Hooper's answer) with some header checking safeguards to handle it all:

def appendDFToCSV_void(df, csvFilePath, sep=","):    import os    if not os.path.isfile(csvFilePath):        df.to_csv(csvFilePath, mode='a', index=False, sep=sep)    elif len(df.columns) != len(pd.read_csv(csvFilePath, nrows=1, sep=sep).columns):        raise Exception("Columns do not match!! Dataframe has " + str(len(df.columns)) + " columns. CSV file has " + str(len(pd.read_csv(csvFilePath, nrows=1, sep=sep).columns)) + " columns.")    elif not (df.columns == pd.read_csv(csvFilePath, nrows=1, sep=sep).columns).all():        raise Exception("Columns and column order of dataframe and csv file do not match!!")    else:        df.to_csv(csvFilePath, mode='a', index=False, sep=sep, header=False)

Thank to Andy, the complete solution:

f = open(filename, 'a') # Open file as append modedf.to_csv(f, header = False)f.close()

• python
• csv
• pandas
• dataframe