问题描述
我有以下代码失败并出现以下错误:
I have the following piece of code which fails with the following error:
RuntimeError: 超出最大递归深度
RuntimeError: maximum recursion depth exceeded
我试图重写它以允许尾递归优化 (TCO).我相信如果发生了 TCO，这段代码应该是成功的.
I attempted to rewrite this to allow for tail recursion optimization (TCO). I believe that this code should have been successful if a TCO had taken place.
def trisum(n, csum):
if n == 0:
return csum
else:
return trisum(n - 1, csum + n)
print(trisum(1000, 0))
我应该断定 Python 不会产生任何类型的 TCO，还是只需要以不同的方式定义它?
Should I conclude that Python does not do any type of TCO, or do I just need to define it differently?
推荐答案
没有，以后也不会了 Guidovan Rossum 更喜欢能够有适当的回溯:
No, and it never will since Guido van Rossum prefers to be able to have proper tracebacks:
尾递归消除 (2009-04-22)
Tail Recursion Elimination (2009-04-22)
尾调用的最后一句话 (2009-04-27)
Final Words on Tail Calls (2009-04-27)
您可以通过如下转换手动消除递归:
You can manually eliminate the recursion with a transformation like this:
>>> def trisum(n, csum):
... while True: # Change recursion to a while loop
... if n == 0:
... return csum
... n, csum = n - 1, csum + n # Update parameters instead of tail recursion
>>> trisum(1000,0)
500500
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