[Python-ideas] Let’s make escaping in f-literals impossible

[Eric V. Smith]

On 8/18/2016 3:15 PM, Terry Reedy wrote:
> On 8/18/2016 12:50 PM, Steve Dower wrote:
> I find it hard to not read f'{x.partition(' + ')[0]}' as string
> concatenation.
>
>> and it will certainly be easier for highlighters
>> to handle (assuming they're doing anything more complicated than simply
>> displaying the entire expression in a different colour).
>
> Without the escapes, existing f-unaware highlighters like IDLE's will be
> broken in that they will highlight the single f-string as two strings
> with differently highlighted content in the middle.  For
> f'{x.partition('if')[0]}', the 'if' is and will be erroneously
> highlighted as a keyword.  I consider this breakage unacceptible.

Right. Because all strings (regardless of prefixes) are first parsed as 
strings, and then have their prefix "operator" applied, it's easy for a 
parser to ignore any sting prefix character.

So something that parses or scans a Python file and currently 
understands u, b, and r to be string prefixes, just needs to add f to 
the prefixes it uses, and it can now at least understand f-strings (and 
fr-strings). It doesn't need to implement a full-blown expression parser 
just to find out where the end of a f-string is.

Eric.