Python：为什么unittest assertEqual会在这些列表上抛出错误而不是失败？

Question

Python 2.7和3.4：为什么test_unexpected_error测试会抛出错误而不是失败？

import unittest


class TestLists(unittest.TestCase):

    def test_unexpected_error(self):
        self.assertEqual([0] * 1000 + [1], [1] + [0] * 1000)

    def test_fails_as_expected(self):
        self.assertEqual([0] * 1000 + [1], [0] * 1000 + [0])


if __name__ == '__main__':
    unittest.main()

错误是：

RuntimeError: maximum recursion depth exceeded while calling a Python object

回溯（删节 - 递归错误是一个递归错误是一个递归错误是....）

Traceback (most recent call last):
  File "sotest.py", line 7, in test_unexpected_error
    self.assertEquals([0] * 1000 + [1], [1] + [0] * 1000)
  File "/usr/lib/python2.7/unittest/case.py", line 513, in assertEqual
    assertion_func(first, second, msg=msg)
  File "/usr/lib/python2.7/unittest/case.py", line 743, in assertListEqual
    self.assertSequenceEqual(list1, list2, msg, seq_type=list)
  File "/usr/lib/python2.7/unittest/case.py", line 722, in assertSequenceEqual
    pprint.pformat(seq2).splitlines()))
  File "/usr/lib/python2.7/difflib.py", line 920, in compare
    for line in g:
  File "/usr/lib/python2.7/difflib.py", line 1038, in _fancy_replace
    for line in self._fancy_helper(a, best_i+1, ahi, b, best_j+1, bhi):
  File "/usr/lib/python2.7/difflib.py", line 1051, in _fancy_helper
    for line in g:
  File "/usr/lib/python2.7/difflib.py", line 1038, in _fancy_replace
    for line in self._fancy_helper(a, best_i+1, ahi, b, best_j+1, bhi):
  File "/usr/lib/python2.7/difflib.py", line 1051, in _fancy_helper
    for line in g:
  File "/usr/lib/python2.7/difflib.py", line 1038, in _fancy_replace
    for line in self._fancy_helper(a, best_i+1, ahi, b, best_j+1, bhi):
  File "/usr/lib/python2.7/difflib.py", line 1051, in _fancy_helper
    for line in g:

(...)

  File "/usr/lib/python2.7/difflib.py", line 965, in _fancy_replace
    cruncher = SequenceMatcher(self.charjunk)
  File "/usr/lib/python2.7/difflib.py", line 219, in __init__
    self.set_seqs(a, b)
  File "/usr/lib/python2.7/difflib.py", line 231, in set_seqs
    self.set_seq2(b)
  File "/usr/lib/python2.7/difflib.py", line 285, in set_seq2
    self.__chain_b()
  File "/usr/lib/python2.7/difflib.py", line 318, in __chain_b
    for i, elt in enumerate(b):
RuntimeError: maximum recursion depth exceeded while calling a Python object

Answer 1

这看起来是一个已知的bug。

如果您不希望单元测试在失败时显示列表之间的差异，则可以执行此备用测试：

self.assertTrue([0] * 1000 + [1] == [1] + [0] * 1000)