signed to unsigned

[Brad Tilley]

In C or C++, I can do this for integer conversion:

unsigned int j = -327681234; // Notice this is signed.

j will equal 3967286062. I thought with Python that I could use struct
to pack the signed int as an unsigned int, but that fails:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
struct.error: integer out of range for 'I' format code

Is there an easy way in Python to do the same conversion that C or C++
code does? Thanks for any advice.

 

[Chris Rebert]

In C or C++, I can do this for integer conversion:

unsigned int j = -327681234; // Notice this is signed.

j will equal 3967286062. I thought with Python that I could use struct
to pack the signed int as an unsigned int, but that fails:

Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
struct.error: integer out of range for 'I' format code

Is there an easy way in Python to do the same conversion that C or C++
code does? Thanks for any advice.

Pack it as the actual type, then unpack it as the desired type:

Python 2.7.1 (r271:86832, Jul 31 2011, 19:30:53)
Type "help", "copyright", "credits" or "license" for more information.(3967286062,)

I would think there's some more efficient way to do this though.

Cheers,
Chris

 

[Brad Tilley]

Pack it as the actual type, then unpack it as the desired type:

Python 2.7.1 (r271:86832, Jul 31 2011, 19:30:53)
Type "help", "copyright", "credits" or "license" for more information.>>> from struct import pack, unpack

(3967286062,)

I would think there's some more efficient way to do this though.

Cheers,
Chris

Thanks Chris! I was doing it backwards. I only have a few of these
right now, so performance isn't a concern. I appreciate the advice.

Brad

 

[Peter Otten]

In C or C++, I can do this for integer conversion:

unsigned int j = -327681234; // Notice this is signed.

j will equal 3967286062. I thought with Python that I could use struct
to pack the signed int as an unsigned int, but that fails:

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
struct.error: integer out of range for 'I' format code

Is there an easy way in Python to do the same conversion that C or C++
code does? Thanks for any advice.

3967286062

 

[Brad Tilley]

3967286062

Very nice! Thanks for that example. Unsigned long longs:

0xffffffffffffffff & -9151314442815602945
9295429630893948671L

 

[Dave Angel]

Very nice! Thanks for that example. Unsigned long longs:

0xffffffffffffffff& -9151314442815602945
9295429630893948671L

Or more generally, use modulo

-13452324 % 2^64