[Python-Dev] PEP 460 reboot

Guido van Rossum guido at python.org
Mon Jan 13 22:56:44 CET 2014

On Mon, Jan 13, 2014 at 1:40 PM, Antoine Pitrou <solipsis at pitrou.net> wrote:
> On Mon, 13 Jan 2014 13:32:28 -0800
> Guido van Rossum <guido at python.org> wrote:
>> But formatb() feels absurd to me. PEP 460 has neither a precise
>> specification or any actual examples, so I can't tell whether the
>> intention is that the format string can *only* contain {...} sequences
>> or whether it can also contain "regular" characters. Translating to
>> formatb(), my question comes down to the legality of the following
>> example:
>>   b'Hello, {}'.formatb(name)  # Where name is some bytes object
> Yes, it's allowed. But so is:
>   b'\xff\x00{}\x85{}'.formatb(payload, trailer)
> The ASCII bias is because of the bytes literal notation.

But it is nevertheless there. Including arbitrary hex bytes in the
ASCII range should be a liability, unless you have memorized the hex
codes for ASCII and know that e.g. '\x25' is '%' and '\x7b' is '{'.

The above example (is it from a real protocol?) would be just as clear
or clearer written as

b'\xff\x00' + payload + b'\x85' + trailer


b''.join([b'\xff\x00', payload, b'\x85', trailer])

and reasoning about those versions requires no understanding of ASCII.

--Guido van Rossum (python.org/~guido)

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