[Python-Dev] RFC: PEP 460: Add bytes % args and bytes.format(args) to Python 3.5

Georg Brandl g.brandl at gmx.net
Fri Jan 10 22:09:18 CET 2014

Am 10.01.2014 18:56, schrieb Eric V. Smith:
> On 1/10/2014 12:17 PM, Juraj Sukop wrote:
>> (Sorry if this messes-up the thread order, it is meant as a reply to the
>> original RFC.)
>> Dear list,
>> newbie here. After much hesitation I decided to put forward a use case
>> which bothers me about the current proposal. Disclaimer: I happen to
>> write a library which is directly influenced by this.
>> As you may know, PDF operates over bytes and an integer or
>> floating-point number is written down as-is, for example "100" or "1.23".
>> However, the proposal drops "%d", "%f" and "%x" formats and the
>> suggested workaround for writing down a number is to use
>> ".encode('ascii')", which I think has two problems:
>> One is that it needs to construct one additional object per formatting
>> as opposed to Python 2; it is not uncommon for a PDF file to contain
>> millions of numbers.
>> The second problem is that, in my eyes, it is very counter-intuitive to
>> require the use of str only to get formatting on bytes. Consider the
>> case where a large bytes object is created out of many smaller bytes
>> objects. If I wanted to format a part I had to use str instead. For example:
>>     content = b''.join([
>>         b'header',
>>         b'some dictionary structure',
>>         b'part 1 abc',
>>         ('part 2 %.3f' % number).encode('ascii'),
>>         b'trailer'])
> I agree. I don't see any reason to exclude int and float. See Guido's
> messages http://bugs.python.org/issue3982#msg180423 and
> http://bugs.python.org/issue3982#msg180430 for some justification and
> discussion. Since converting int and float to strings generates a very
> small range of ASCII characters, ([0-9a-fx.-=], plus the uppercase
> versions), what problem is introduced by allowing int and float? The
> original str.format() work relied on this fact in its stringlib
> implementation.

I agree.

I would have needed bytes-formatting (with numbers) recently writing .rtf files.


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