for loop: range() result has too many items

[Mark Dickinson]

On Oct 13, 10:39 pm, Steven D'Aprano
<ste... at REMOVE.THIS.cybersource.com.au> wrote:
> On Tue, 13 Oct 2009 16:17:58 -0500, Peng Yu wrote:
> > Hi,
>
> > The following code does not run because range() does not accept a big
> > number.
>
> Incorrect.
>
> >>> range(sys.maxint+2, sys.maxint+5)
>
> [2147483649L, 2147483650L, 2147483651L]

For what it's worth, there *is* a Python oddity lurking
under the surface here, at least for 64-bit.  Here's
Python 2.6 on a 64-bit machine:

>>> range(2**31-1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
MemoryError
>>> range(2**31)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OverflowError: range() result has too many items

The first call tries to allocate a list containing
2**31-1 integers.  At 32 bytes per entry (8 for the
list pointer, 24 for the integer itself), that's not
surprising on a machine with < 64 Gb of memory.

The second call, however, doesn't even try to
allocate the memory, but decides that the range can't
be represented.  That's not right:  this is an LP64
machine, so the size of the list can be represented,
and the start, stop and step values are representable
as C longs (which is what CPython uses internally for
this purpose).  On a machine with >64 Gb of memory,
this call should succeed.  On an LP64 machine with
<64 Gb of memory, it should produce MemoryError, not
OverflowError.

Mark