new_contents: 
  import argparse
  import http.client
  import pprint
  
  from . import exceptions
  from . import git_requester
  from . import guess_lang
  
  
  def main():
      parser = argparse.ArgumentParser("git-lang-guesser")
      parser.add_argument("username")
      parser.add_argument("--list-all", action="store_true")
  
      args = parser.parse_args()
      username = args.username
      list_all = args.list_all
  
      try:
          repos = git_requester.get_public_repos_for_user(username)
      except exceptions.RequestFailed as exc:
          if exc.response.status_code == http.client.NOT_FOUND:
              print("User {0} not found".format(username))
              exit(1)
          else:
              print("HTTP error code {0}: {1}".format(exc.response.status_code, exc.response.text))
              exit(1)
          repos = []  # silence PyCharm warning
  
      if not repos:
          print("User does not have any public repos")
          exit(1)
  
      if list_all:
          counter = guess_lang.count_languages(repos, filter_none=False)
          pprint.pprint(dict(counter))
      else:
          favourite = guess_lang.guess_favourite(repos)
          print(favourite)
  
  if __name__ == "__main__":
      main()
subject: Add a main function with top-level logic