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The fix is fine (it works for me the same way as for Tim), but I think we're shooting past the problem here.

First, pdb doesn't use repr.repr(), it uses the normal builtin repr().

Second, I don't see any sluggishness in pdb with large arrays. I tried
debugging
def foo():
    a = range(8000000)
and there was no problem. Allocating the object took a bit of time, yes, and if you actually try to print it you'll stare at about 800K lines filled with digits scrolling over your screen, but that is to be expected.

Could it be your sluggishness is coming from something else? For example, MacOSX starts behaving *very* badly if your root disk is full, because then it can't allocate swap space, and due to its optimistic behaviour it comes to a grinding halt.