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Editorial Team
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Asked: 2026-05-13T13:29:22+00:00

So, cPython (2.4) has some interesting behaviour when the length of something gets near

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So, cPython (2.4) has some interesting behaviour when the length of something gets near to 1<<32 (the size of an int). 

r = xrange(1<<30)
assert len(r) == 1<<30

is fine, but:

r = xrange(1<<32)
assert len(r) == 1<<32
ValueError: xrange object size cannot be reported`__len__() should return 0 <= outcome

Alex’s wowrange has this behaviour as well. wowrange(1<<32).l is fine, but len(wowrange(1<<32)) is bad. I’m guessing there is some floating point behaviour (being read as negative) action going on here.

  1. What exactly is happening here? (this is pretty well-solved below!)
  2. How can I get around it? Longs?

(My specific application is random.sample(xrange(1<<32),ABUNCH)) if people want to tackle that question directly!)

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1 Answer

  1. Editorial Team

    cPython assumes that lists fit in memory. This extends to objects that behave like lists, such as xrange. essentially, the len function expects the __len__ method to return something that is convertable to size_t, which won’t happen if the number of logical elements is too large, even if those elements don’t actually exist in memory.

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