Write Data from Multiple Files to a Master File in Python

File handling is an important part of any web application.

Python has several functions for creating, reading, updating, and deleting files.

To write to an existing file, you must add a parameter to the open()function −

"a" − Append − will append to the end of the file

"w" − Write − will overwrite any existing content

Example

import os
# list the files in directory
lis = os.listdir('D:\python' '\data_files\data_files')
print(lis)
tgt = os.listdir('D:\python' '\data_files\target_file')  
file_dir ='D:\python\data_files\data_files'
out_file = r'D:\python\data_files\target_file\master.txt'
ct = 0  
print('target file :', tgt)
try:
   # check for if file exists
   # if yes delete the file
   # otherwise data will be appended to existing file
   if len(tgt)>0:
      os.remove('D:\python' '\data_files\target_file\master.txt')
      open(tgt, 'a').close()
   else:
      # create an empty file
      open(tgt, 'a').close()
except:
   head = open('D:\python' '\data_files\target_file\master.txt', 'a+')
   line ='empno, ename, sal'
   # write header to output
   print(head, line)
   head.close()
   # below loop to write data to output file
   for line1 in lis:
      f_dir = file_dir+'\'+line1
      # open files in read mode
      in_file = open(f_dir, 'r+')
      # open output in append mode
      w = open(out_file, 'a+')
      d = in_file.readline()
      d = in_file.readlines()
      w.write("\n")
      for line2 in d:
         print(line2)
         w.write(line2)    
      ct = ct + 1  
   w.close()      
#using pandas
import pandas as pd
# pd.read_csv creates dataframes
df1 = pd.read_csv('D:\python\data_files\data_files\emp_1.txt')
df2 = pd.read_csv('D:\python\data_files\data_files\emp_2.txt')
df3 = pd.read_csv('D:\python\data_files\data_files\emp_3.txt')
frames = [df1, df2, df3]
# concat function concatenates the frames
result = pd.concat(frames)
# to_csv function writes output to file
result.to_csv('D:\python\data_files' '\target_file\master.txt', encoding ='utf-8', index = False)