old_contents: #!/usr/bin/env python
  
  from lexer import read_code, remove_comments, tokenize
  from builtin_functions import builtin_functions
  from evaluate_list import evaluate_list
  
  if __name__ == '__main__':
  	code = read_code()
  	code = remove_comments(code)
  
  	tokens = tokenize(code)
  	evaluate_list(tokens, {}, builtin_functions)
  
new_contents: #!/usr/bin/env python
  
  from lexer import read_code, remove_comments, tokenize
  from builtin_functions import builtin_functions
  from evaluate_list import evaluate_list
  
  if __name__ == '__main__':
  	try:
  		code = read_code()
  		code = remove_comments(code)
  
  		tokens = tokenize(code)
  		evaluate_list(tokens, {}, builtin_functions)
  	except Exception as exception:
  		print('Error: {!s}.'.format(exception))
  
subject: add a errors handling.