On 8/14/2019 11:02 AM, Random832 wrote:
On Mon, Aug 12, 2019, at 15:15, Terry Reedy wrote:
Please no more combinations. The presence of both legal and illegal
combinations is already a mild nightmare for processing and testing.
idlelib.colorizer has the following re to detest legal combinations
stringprefix = r"(?i:r|u|f|fr|rf|b|br|rb)?"
More advanced syntax highlighting editors have to handle each string type separately
anyway, because they highlight (valid) backslash-escapes and f-string formatters.
The proposed 'v-string' type would need separate handling even in a simplistic
editor like IDLE, because it's different at the basic level of \" not ending
the string (whereas, for better or worse, all current string types have exactly the
same rules for how to find the end delimiter)
The reason I defined f-strings as I did is so that lexer/parsers
(editors, syntax highlighters, other implementations, etc.) could easily
ignore them, at least as a first pass. They're literally like all other
strings to the lexer. Python's lexer/parser says that a string is:
- some optional letters, making the string prefix
- an opening quote or triple quote
- some optional chars, with \ escaping
- a matching closing quote or triple quote
The parser then validates the string prefix ('f' is okay, 'b' is okay,
'fb' isn't okay, 'x' isn't okay, etc.) It then operates on the contents
of the string, based on what the string prefix tell it to do.
So all an alternate lexer/parser has to do is add 'f' to the valid
string prefixes, and it could then at least skip over f-strings.
Somewhere in my notes I have 3 or 4 examples of projects that did this,
and voila: they "supported" f-strings. Imagine a syntax highlighter that
didn't want to highlight the inside of an f-string.
The proposed v-strings would indeed break this. I'm opposed to them for
this reason, among others.
That all said, I am considering moving f-string parsing into the CPython
parser. That would let you say things like:
f'some text {ord('a')}'
I'm not sure that's a great idea, but I've discussed it with several
alternate implementations, and with authors of several editors, and they
seem okay with it. I'm following Guido's parser experiment with some
interest, to see how it might interact with this proposal. Might they
also be okay with v-strings? Maybe. But it seems like a lot of hassle
for a very minor feature.
Eric
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