On 2018-04-17, Travis Griggs <travisgri...@gmail.com> wrote:
> I posted this on SO, but… yeah…
>
> I'm doing some serial protocol stuff and want to implement a basic
> byte stuffing algorithm in python. Though really what this really
> generalizes to is “what is the most pythonic way to transform one
> sequence of bytes where some bytes are passed through 1:1, but
> others are transformed to longer subsequences of bytes?” I’m pretty
> sure this rules out the use of transform() which expects a 1:1
> mapping.
>
>
> So far, I've come with 5 different approaches, and each of them has something
> I don't like about it:
>
> 1 Via Generator
>
> def stuff1(bits):
> for byte in bits:
> if byte in _EscapeCodes:
> yield PacketCode.Escape
> yield byte ^ 0xFF
> else:
> yield byte
>
> This may be my favorite, but maybe just because I'm kind of
> fascinated by yield based generators. I worried that the generator
> would make it slow, but it's actually the second fastest of the
> bunch.
I find that the most readible, and would certainly get my vote -- even
if it was the slowest (unless it was so slow as to be a problem).
[...]
> def stuff5(bits):
> escapeStuffed = bytes(bits).replace(bytes([PacketCode.Escape]),
> bytes([PacketCode.Escape, PacketCode.Escape ^ 0xFF]))
> stopStuffed= escapeStuffed.replace(bytes([PacketCode.Stop]),
> bytes([PacketCode.Escape, PacketCode.Stop ^ 0xFF]))
> return stopStuffed.replace(bytes([PacketCode.Start]),
> bytes([PacketCode.Escape, PacketCode.Start ^ 0xFF]))
>
> This is the fastest. But I don't like the way the code reads and the
> intermediate sweeps.
Yow, that's ugly -- I don't think I'd be able to tell you what it
actually does without actually running it.
If speed is that important, I might just write a function in C and
call it with ctypes. :)
--
Grant Edwards grant.b.edwards Yow! HAIR TONICS, please!!
at
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