unsigned integer?

[Duncan Booth]

"Jack" <nospam at invalid.com> wrote:

> This is a naive question:
> 
> "%u" % -3
> 
> I expect it to print 3. But it still print -3.

Internally it uses the C runtime to format the number, but if the number 
you ask it to print unsigned is negative it uses %d instead of %u. I have 
no idea if it is actually possibly to get a different output for %d versus 
%u.

> 
> Also, if I have an int, I can convert it to unsigned int in C:
>    int i = -3;
>    int ui = (unsigned int)i;
> 
> Is there a way to do this in Python? 
> 
Depeneding on how exactly you want it converted:

   i = -3
   ui = abs(i)
   print ui
   ui = (i & 0xffff) # for 16 bit integers
   print ui
   ui = (i & 0xffffffff) # for 32 bit integers
   print ui
   ui = (i & 0xffffffffffffffff) # for 64 bit integers
   print ui
   ui = (i & 0xffffffffffffffffffffffffffffffff) # for 128 bit integers
   print ui

which gives the following output:

3
65533
4294967293
18446744073709551613
340282366920938463463374607431768211453

There isn't a unique way to convert a Python integer to an unsigned value 
which is why the %u format string cannot do anything other than print the 
value. Personally I'd have expected the Python one to either print the 
absolute value or throw an exception, but I guess making it an alias for %d 
kind of makes sense as well.