def average(values):
  """Computes the arithmetic mean of a list of numbers.

  > print(average([20, 30, 70]))
  40.0
  """
  return sum(values) / len(values)

import doctest
doctest.testmod(verbose=True)  # doctest.testmod是测试模块，verbose默认是False,意思是出错才用提示；True，对错都有执行结果

Trying:
  print(average([20, 30, 70]))
Expecting:
  40.0
ok
Trying:
  print(average([90, 40, 20]))
Expecting:
  50.0
ok
1 items had no tests:
  __main__
1 items passed all tests:
  2 tests in __main__.average
2 tests in 2 items.
2 passed and 0 failed.
Test passed.
[Finished in 0.5s]