check if input is file, if not make it a file

# Define function to check if string is a file
def is_file(file_name):
  if file_name.endswith('.txt'):
    print(file_name)
    return file_name
  else:
    new_file_name = f'{file_name}.txt'
    print(new_file_name)
    return new_file_name
 
is_file('file1')