How to convert bytearray into integer?

[Thomas Jollans]

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.

> 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.

> c) manually manipulation.

Well, yes, you can do that, but it gets messy when you're working with more 
complex data structures, or you have to consider byte order.

> Are there any other ways?

You could write a C extension module tailored to your specific purpose ;-) 

> number = 1
> 1.00135803223e-05
> 1.00135803223e-05
> 5.96046447754e-06
> -----
> 
> As the number of benchmarking loops decreasing, method c which is
> manually manipulating overwhelms the former 2 methods.  However, if
> number == 10K, the struct method wins.
> 
> Why does it happen?

struct wins because it's built for the job.

As for the small numbers: don't take these numbers seriously. Just don't. This 
may be caused by the way your OS's scheduler handles things for all I know. If 
there is an explanation for this unscientific observation, I have two guesses 
what it might be:
 * struct and ctypes still need to do some setup work, or something
 * somebody is optimising something, but doesn't know what they should be
   optimising in the first place after only a few iterations.