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

[Eric V. Smith]

On 8/19/2016 1:16 AM, Terry Reedy wrote:
> On 8/18/2016 8:27 PM, Eric V. Smith wrote:
>> 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.
>
> Indeed, IDLE has one prefix re, which has changed occasionally and which
> I need to change for 3.6, and 4 res for the 4 unprefixed strings, which
> have been the same, AFAIK, for decades.  It that prefixes all 4 string
> res with the prefix re and o or's the results together to get the
> 'string' re.

For something else that would become significantly more complicated to 
implement, you need look no further than the stdlib's own tokenizer 
module. So Python itself would require changes to parsers/lexers in 
Python/ast.c, IDLE, and Lib/tokenizer.py. In addition it would require 
adding tokens to Include/tokens.h and the generated Lib/token.py, and 
everyone using those files would need to adapt.

Not that it's impossible, of course. But don't underestimate the amount 
of work this proposal would cause to the many places in and outside of 
Python that examine Python code.

Eric.