Here’s what a ‘copy-n-paste’ in a moment of hurry can cause. This typo
wen’t unnoticed for almost a whole day, and then I stared at the
result for about a minute, wondering if I had been slashdotted. This
code was in a the statistics counter of a experimental cache manager I
wrote this morning (more about the cache manager when I recover):

>>> h = [0]
>>> h[0] += h[0] + 1; h
[1]
>>> h[0] += h[0] + 1; h
[3]
>>> h[0] += h[0] + 1; h
[7]
>>> h[0] += h[0] + 1; h
[15]
>>> h[0] += h[0] + 1; h
[31]
>>> h[0] += h[0] + 1; h
[63]