[Python-ideas] format specifier for "not bytes"

[Daniel Holth]

On Wed, Aug 29, 2012 at 6:30 PM, Mathias Panzenböck
<grosser.meister.morti at gmx.net> wrote:
> On 08/27/2012 04:34 PM, Barry Warsaw wrote:
>>
>> On Aug 25, 2012, at 09:16 AM, Nick Coghlan wrote:
>>
>>> A couple of people at PyCon Au mentioned running into this kind of issue
>>> with Python 3. It relates to the fact that:
>>> 1. String formatting is *coercive* by default
>>> 2. Absolutely everything, including bytes objects can be coerced to a
>>> string, due to the repr() fallback
>>>
>>> So it's relatively easy to miss a decode or encode operation, and end up
>>> interpolating an unwanted "b" prefix and some quotes.
>>>
>>> For existing versions, I think the easiest answer is to craft a regex
>>> that
>>> matches bytes object repr's and advise people to check that it *doesn’t*
>>> match their formatted strings in their unit tests.
>>>
>>> For 3.4+ a non-coercive string interpolation format code may be
>>> desirable.
>>
>>
>> Or maybe just one that calls __str__ without a __repr__ fallback?
>>
>
>>>> b'a'.__str__()
> "b'a'"
>
> __str__ still returns the bytes literal representation.
>
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This is now a patch at http://bugs.python.org/issue18373. The user can
call sys.getbyteswarning() and sys.setbyteswarning(integer) to control
whether str(bytes) warns in the current thread, but you also have to
adjust the warnings module for it to be useful.