How to convert bytearray into integer?

Jacky jacky.chao.wang at gmail.com
Tue Aug 17 03:00:09 CEST 2010


On Aug 17, 3:38 am, Thomas Jollans <tho... at jollybox.de> wrote:
> On Monday 16 August 2010, it occurred to Jacky to exclaim:
>
>
>
>
>
> > Hi Thomas,
>
> > Thanks for your comments!  Please check mine inline.
>
> > On Aug 17, 1:50 am, Thomas Jollans <tho... at jollybox.de> wrote:
> > > On Monday 16 August 2010, it occurred to Jacky to exclaim:
> > > > Hi there,
>
> > > > Recently I'm facing a problem to convert 4 bytes on an bytearray into
> > > > an 32-bit integer.  So far as I can see, there're 3 ways:
> > > > a) using struct module,
>
> > > Yes, that's what it's for, and that's what you should be using.
>
> > My concern is that struct may need to parse the format string,
> > construct the list, and de-reference index=0 for this generated list
> > to get the int out.
>
> > There should be some way more efficient?
>
> The struct module is written in C, not in Python. It does have to parse a
> string, yes, so, if you wrote your own, limited, C function to do the job, it
> might be marginally faster.
>
>
>
> > > > b) using ctypes module, and
>
> > > Yeeaah, that would work, but that's really not what it's for. from_buffer
> > > wants a writable buffer interface, which is unlikely to be what you want.
>
> > Actually my buffer is writable --- it's an bytearray.  Turning it into
> > a R/O one make me to do extra effort: wrapping the bytearray into
> > buffer().
>
> > My question is, this operation seems like to be much simpler than the
> > former one, and it's very straightforward as well.  Why is it slow?
>
> Unlike struct, it constructs an object you're not actually interested in
> around your int.
>
> > it's hard to image why socket object provides the interface:
> > socket.recv_from(buf[, num_bytes[, flags]]) but forget the more
> > generic one: socket.recv_from(buf[, offset[, num_bytes[, flags]]])
>
> Well, that's what pointer arithmetic (in C) or slices (in Python) are for!
> There's an argument to be made for sticking close to the traditional
> (originally C) interface here - it's familiar.

Hi Thomas, - I'm not quite follow you.  It will be great if you could
show me some code no this part...

>
>  - Thomas- Hide quoted text -
>
> - Show quoted text -




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