[Python-Dev] Should PEP 498 specify if rf'...' is valid?

[Martin Panter]

On 26 October 2015 at 19:43, MRAB <python at mrabarnett.plus.com> wrote:
> On 2015-10-26 18:45, Sven R. Kunze wrote:
>>
>> On 26.10.2015 16:22, Ethan Furman wrote:
>>>
>>> On 10/23/2015 08:20 AM, Nick Coghlan wrote:
>>>>
>>>> My own objection isn't to allowing "fR" or "fbR", it's to
>>>> allowing the uppercase "F".
>>>>
>>>> I also don't understand why we can't say "if 'f' is part of a
>>>> string prefix, it must be first".
>>>
>>>
>>> Sometimes order matters, and sometimes it does not.  If the order
>>> does not have an impact on the final code, it does not matter, and
>>> making us have to remember an order that does not matter is a
>>> waste.
>>
>>
>> Order that matters? You must be kidding. That would turn different
>> types of string extremely hard to understand because semantics
>> differ.
>>
>> That is, btw., one reason, why I favor a fixed order (alphabetically
>> or something). Easy to remember and no way to misinterpret it.
>>
> In Python 2, how often have you seen prefix "ur" rather than "ru"?
>
> I always used "ur".
>
> How often is alphabetical order used in the prefixes?
>
> If the order isn't alphabetical, then it's going to be some order
> that's harder to remember, so I agree with Ethan here.

In Python 2, ru". . ." is a SyntaxError, despite R coming before U in
the alphabet. And rb". . ." is also a SyntaxError, but in Python 3 it
was made legal.

I don’t see much point restricting the order of rf". . ." versus fr".
. .". Neither flag is particularly more important than the other, and
even if one were, should that one be at the front, or at the end
closer to the string?