[ python-Bugs-1003935 ] xrange overflows

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Bugs item #1003935, was opened at 2004-08-05 15:16
Message generated for change (Comment added) made by hfuru
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>Category: Python Interpreter Core
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Hallvard B Furuseth (hfuru)
Assigned to: Nobody/Anonymous (nobody)
Summary: xrange overflows

Initial Comment:
These restrictions are undocumented both in the
xrange doc string and in the reference manual
(Info node 'XRange Type'):

  >>> xrange(maxint, maxint + 10)
  Traceback (most recent call last):
    File "<stdin>", line 1, in ?
  OverflowError: long int too large to convert to int

  >>> xrange(-100, maxint)
  Traceback (most recent call last):
    File "<stdin>", line 1, in ?
  OverflowError: xrange() result has too many items

I hope the overflows below are bugs and not
features.  It works if 3/-3 is replaced with 1/-1:

  >>> xrange(0, maxint, 3)
  Traceback (most recent call last):
    File "<stdin>", line 1, in ?
  OverflowError: integer addition

  >>> xrange(0, -maxint, -3)
  Traceback (most recent call last):
    File "<stdin>", line 1, in ?
  OverflowError: integer addition

Python installation:

  Python 2.3.3 (#1, May 25 2004, 20:22:36) 
  [GCC 3.2.3] on sunos5
  Type "help", "copyright", "credits" or "license"
for    more information.
  >>> from sys import maxint
  >>> "%x" % maxint
  '7fffffff'


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>Comment By: Hallvard B Furuseth (hfuru)
Date: 2004-08-05 17:14

Message:
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user_id=726647

> Do you have a real use case for this?

For the 'hopefully bugs' variants, yes:

#1: Loop forever:

  for i in xrange(x, sys.maxint, y)

That's a lot faster than

  i = x
  while True: ... i += y

#2: 'loop until optional upper bound':

  def some_loop(start, end = sys.maxint):
    for i in xrange(start, end, whatever())

> Do any real apps need to loop over more than
> sys.maxint integers?

The answer may be yes nowadays.  Even my old
Solaris can find primes up to maxint/2 in just
2 hours.  That's a loop over maxint/4 integers.
Though the remaining 3/4 come slower:-)

Still, I expect variants of the above code would
be less uncommon, like some_loop(-100).

> It would be ashamed to muckup the high
> performance implementation for something that
> does not arise in practice.

I hope you do not mean xrange(0, maxint, 3).

If you mean xrange(-100, maxint): Maybe xrange
could be split in several types (fast and slower)
and the xrange() operator would return one of
these, similar to how int() now can return long?


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Comment By: Martin v. Löwis (loewis)
Date: 2004-08-05 17:12

Message:
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The OverflowErrors are definitely intentional, and by
design. xrange() is documented as working the same way as
range(), so any error in the documentation is an error in
the range() documentation.

Reclassifying this as a documentation bug.

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Comment By: Raymond Hettinger (rhettinger)
Date: 2004-08-05 15:49

Message:
Logged In: YES 
user_id=80475

Do you have a real use case for this?  Do any real apps need
to loop over more than sys.maxint integers?  It would be
ashamed to muckup the high performance implementation for
something that does not arise in practice.

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