hex(-5) => Futurewarning: ugh, can't we have a better hex than '-'[:n<0]+hex(abs(n)) ??

[Jeff Epler]

On Mon, Aug 18, 2003 at 07:56:42AM +0300, Juha Autero wrote:
> Two questions: What is the best way to generate bitmask of n bits all
> ones?

    def ones(n):
        r = (1l << n) - 1
        try:
            r = int(r)
        except OverflowError:
            pass
        return r

does this do what you want?  It gives these results:

# 2.3b1 (old, but should have 2.3's long vs int quirks)
>>> for i in (0, 1, 2, 3, 31, 32, 33, 63, 64, 65):
...     print "%2s %22s %22s" % (i, `ones(i)`, hex(ones(i)))
... 
 0                      0                    0x0
 1                      1                    0x1
 2                      3                    0x3
 3                      7                    0x7
31             2147483647             0x7fffffff
32            4294967295L            0xFFFFFFFFL
33            8589934591L           0x1FFFFFFFFL
63   9223372036854775807L    0x7FFFFFFFFFFFFFFFL
64  18446744073709551615L    0xFFFFFFFFFFFFFFFFL
65  36893488147419103231L   0x1FFFFFFFFFFFFFFFFL

# 2.2.2
>>> for i in (0, 1, 2, 3, 31, 32, 33, 63, 64, 65):
...     print "%2s %22s %22s" % (i, `ones(i)`, hex(ones(i)))
... 
 0                      0                    0x0
 1                      1                    0x1
 2                      3                    0x3
 3                      7                    0x7
31             2147483647             0x7fffffff
32            4294967295L            0xFFFFFFFFL
33            8589934591L           0x1FFFFFFFFL
63   9223372036854775807L    0x7FFFFFFFFFFFFFFFL
64  18446744073709551615L    0xFFFFFFFFFFFFFFFFL
65  36893488147419103231L   0x1FFFFFFFFFFFFFFFFL