[Tutor] Workaround for limitation in xrange()?

[Danny Yoo]

> >>> for x in xrange(2**31):
>     pass
>
> Traceback (most recent call last):
>   File "<pyshell#16>", line 1, in <module>
>     for x in xrange(2**31):
> OverflowError: long int too large to convert to int


Hi Dick,

Hmmm... I'd consider this a misfeature in the implementation.  Apparently 
xrange (and range) must be built with regular ints, not long ints.  This 
limitation is documented, although I think this is inconsistent and a bad 
thing.

     http://www.python.org/doc/2.3.5/lib/built-in-funcs.html#l2h-73
     http://www.python.org/doc/2.3.5/lib/built-in-funcs.html#l2h-55


In the meantime, you can build your own version of xrange that should work 
on long ints.  Here is an example:

#################
def myxrange(m, n=None, skip=1):
     """An xrange-like function that can deal with long ints.
     Note: doesn't deal with negative ranges particularly well."""
     if n is None:
        m, n = 0, m
     i = m
     while i < n:
         yield i
         i = i + skip
#################


This is a "generator" that does pretty much what you'll want.

##################################################################
>>> list(myxrange(1, 5))
[1, 2, 3, 4]
>>> list(myxrange(2**32, 2**32 + 5))
[4294967296L, 4294967297L, 4294967298L, 4294967299L, 4294967300L]
##################################################################


Note: this is a quick-and-dirty function; I wouldn't use it in production 
yet.  It needs some more work to reject bad input.  If you want, we can 
talk about exhaustively testing the function using robust equivalence 
class testing.  *grin*


Best of wishes!