int vs long

[Nick Craig-Wood]

Gabriel Genellina <gagsl-py2 at yahoo.com.ar> wrote:
>  En Sun, 16 Dec 2007 20:28:02 -0300, Troels Thomsen <"nej  
>  tak..."@bag.python.org> escribi?:
> 
> >
> > The readFile function from the win32 package aparently really expect an
> > integer :
> >
> >     def inWaiting(self):
> >         """Returns the number of bytes waiting to be read"""
> >         flags, comstat = ClearCommError(self.__handle)
> >         return comstat.cbInQue
> >
> > ReadFile(h, s.inWaiting())
> >
> > My code crashes because inWaiting returns a long, not an int
> 
>  That's very strange. The cbInQue field is a DWORD in C, seen as an int in  
>  Python. How do you know it returns a long?
> 
> > Why is that different on my machine and my collegues ? Have I or he
> > installed a wrong version of a package?
> > CPython 2.5.
> 
>  And pywin32 build 210, I presume.
> 
> > Was not expecting int<->long type problems in excactly python language.
> > Is that because we are navigating so close to the win32 api that the  
> > types
> > are more strictly enforced ?
> 
>  Somewhat. At the API level, function arguments have to be converted to  
>  native C types, like ReadFile expecting a DWORD. Any number greater than  
>  2**32 won't fit, but I can't think how such thing could happen looking at  
>  those few posted code lines.

Actually any number >= 2**31 won't fit in a python int.

  >>> 2**31
  2147483648L

According to my headers DWORD is defined like this

  typedef unsigned long DWORD;

So you might see longs returned when you expected ints if the result
was >= 0x8000000.

-- 
Nick Craig-Wood <nick at craig-wood.com> -- http://www.craig-wood.com/nick