[Python-ideas] Add function readbyte to asyncio.StreamReader

[Gustavo Carneiro]

Well, even if it is worth, i.e. your use case is not rare enough, I would
suggest at least making it private, readexactly can call this specialised
function if nbytes==1:

def _readbyte(self):
   ....

def readexactly(self, num):
   if num == 1:
      return self._readbyte()
  ... the rest stays the same..


But to be honest, you are probably better off managing the buffer yourself:
Just call, e.g., stream.read(4096), it will return a buffer of up to 4k
length, then you can iterate over the buffer byte by byte until the
condition is met, repeat until the end of stream, or whatever.


On Sun, 22 Jul 2018 at 12:11, Jörn Heissler <python-ideas-2018 at tutnicht.de>
wrote:

> Hello,
>
> I'm implementing a protocol where I need to read individual bytes until
> a condition is met (value & 0x80 == 0).
>
> My current approach is: value = (await reader.readexactly(1))[0]
>
> To speed this up, I propose that a new function is added to
> asyncio.StreamReader: value = await reader.readbyte()
>
> I duplicated readexactly and stripped out some parts. Below code appears
> to work:
>
>     async def readbyte(self):
>         if self._exception is not None:
>             raise self._exception
>
>         while not self._buffer:
>             if self._eof:
>                 raise EOFError()
>             await self._wait_for_data('readbyte')
>
>         data = self._buffer[0]
>         del self._buffer[0]
>         self._maybe_resume_transport()
>         return data
>
> For comparing the speed, I'm receiving a 50 MiB file byte-by-byte.
>
> cpython-3.7.0:
>     readexactly: 42.43 seconds
>     readbyte   : 22.05 seconds
>     speedup    : 92.4%
>
> pypy3-v6.0.0:
>     readexactly: 3.21 seconds
>     readbyte   : 2.76 seconds
>     speedup    : 16.3%
>
> Thanks
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-- 
Gustavo J. A. M. Carneiro
Gambit Research
"The universe is always one step beyond logic." -- Frank Herbert
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