处理超出最大递归深度

Question

我创建了一个使用递归来解决简单迷宫的程序。如果出现相当复杂的迷宫，我会得到最大递归深度误差。我已经在这个网站上搜索了那个错误并阅读了主题，所以我相信我对正在发生的事情有一个大致的了解。

与我看到的其他线程不同，我并不想增加递归限制。 sys.setrecursionlimit() 不是我要找的。我希望能够处理溢出，而不是崩溃让程序打印一条消息（print("Sorry but this maze solver was not able to finish analyzing the maze due to recursion limits)）并关闭。

我知道使用 try 和 except 来处理错误，但我不确定是否可以合并它来处理最大递归深度错误。

Answer 1

最大递归深度错误只是另一个例外；你可以赶上RecursionError exception（Python 3.5 或更高版本）：

try:
    solveMaze(maze)
except RecursionError as re:
    print('Sorry but this maze solver was not able to finish '
          'analyzing the maze: {}'.format(re.args[0]))

我已将附加到运行时异常的错误消息合并；对于 maximum recursion depth exceeded 的递归错误。

如果需要支持 3.5 之前的 Python 版本，可以捕获基类 RuntimeError。如果您担心捕获不是递归深度错误的运行时错误，您可以自省.args[0] 值：

try:
    solveMaze(maze)
except RuntimeError as re:
    if re.args[0] != 'maximum recursion depth exceeded':
        # different type of runtime error
        raise
    print('Sorry but this maze solver was not able to finish '
          'analyzing the maze: {}'.format(re.args[0]))

选项演示：

>>> def infinity(): return infinity()
... 
>>> try:
...     infinity()
... except RecursionError as re:
...     print('Oopsie: {}'.format(re.args[0]))
... 
Oopsie: maximum recursion depth exceeded
>>> def alter_dict_size():
...     dct = {'foo': 'bar'}
...     for key in dct:
...         del dct['foo']
... 
>>> try:
...     alter_dict_size()
... except RuntimeError as re:
...     print('Oopsie: {}'.format(re.args[0]))
... 
Oopsie: dictionary changed size during iteration
>>> try:
...     infinity()
... except RuntimeError as re:
...     if re.args[0] != 'maximum recursion depth exceeded':
...         raise
...     print('Oopsie: {}'.format(re.args[0]))
... 
Oopsie: maximum recursion depth exceeded
>>> try:
...     alter_dict_size()
... except RuntimeError as re:
...     if re.args[0] != 'maximum recursion depth exceeded':
...         raise
...     print('Oopsie: {}'.format(re.args[0]))
... 
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
  File "<stdin>", line 3, in alter_dict_size
RuntimeError: dictionary changed size during iteration

更改字典大小也会引发RuntimeError 异常，但测试生成的异常消息可以让您区分。