I recently wrote a python script to convert multiple files EOL’s from Unix to DOS and vice versa.

I am looking for tips to improve my code or if there is a better way of doing something that I have missed.

#!/usr/bin/env python3  import sys  def main():     command, *filenames = sys.argv[1:]     valid_commands = ['-d', '-u']     sys.tracebacklimit = None      if not command in valid_commands:         error = """'{command}'         Provide the following arguments -u|d file [file2] [file3] ...         flags:             -u : converts DOS to UNIX             -d : converts UNIX to DOS         example command:             ./eol -u foo.py bar.py""".format(command=command)          raise ValueError(error)         sys.exit(1)      if filenames:         convert(filenames, command)     else:         print("> no files to convert")  def convert(files, command):     for file in files:         text = open(file, 'r').read()          with open(file, 'w') as current:             if command == '-u':                 format = 'UNIX'                 current.write(text.replace('\r\n', '\n'))             elif command == '-d':                 format = 'DOS'                 current.write(text.replace('\n', '\r\n'))          print("> converting file {filename} to {format} ...".format(               filename=file, format=format))  if __name__ == "__main__":     main()