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

# -*- coding:utf-8 -*-
import os
import time
import pandas as pd
 
from multiprocessing import Pool
 
def merge(filename):
  return pd.read_csv('./fun_data/'+filename)
 
if __name__ == "__main__":
  file_list = os.listdir('./fun_data')
  e1 = time.time()
 
  pool = Pool(20)
  result = pool.map(merge,file_list)
  pool.close()
  pool.join()
 
  e2 = time.time()
  print(e2 - e1)
 
  for i in result:
    i.to_csv('./static.csv',mode='a',encoding='utf-8',header=False,index=False)
  e3 = time.time()
  print(e3-e2)