Brett Cannon <brett@python.org> schrieb am Mi., 17. Aug. 2016 um 19:15 Uhr:

Please don't cross-post as it means anyone replying to your email will now split the conversation as not everyone will be subscribed to all of the mailing lists you sent this to. I have stripped out all but python-dev for my reply.

sorry, i’ll remember that! i just hit reply on the post and didn’t realize it was posted to more than python-dev.

I don't remember specifically seeing any email on this. Do you have a link to your post from the python-ideas archive showing your email actually made it to the list?

i posted here…

I believe you're referring to https://www.python.org/dev/peps/pep-0498/#escape-sequences ?

yes!

how am i going about changing f-literal grammar before the beta hits?

You can post to python-ideas and start a discussion there as the PEP has already been accepted and implemented with the current semantics or ask for clarification for the reasoning behind the decision here on python-dev.

thanks. i’d like to hereby do the latter. i think the PEP’s wording is pretty clear:

Due to Python's string tokenizing rules, the f-string f'abc {a['x']} def' is invalid. The tokenizer parses this as 3 tokens: f'abc {a[' , x , and ']} def' . Just like regular strings, this cannot be fixed by using raw strings. There are a number of correct ways to write this f-string

i guess that means that python’s string tokenization rules are reused for f-literals, even though they aren’t actually strings. could someone please explain if this is right and if so, why it was chosen to do this instead of writing more fitting tokenization code?

naively i’d assume f'abc {a['x']} def' to tokenize as something like:

F_BEGIN
F_STRING_BEGIN "a" "b" "c" " " F_STRING_END
F_EXPR_START
NAME_START "a" NAME_END
GETITEM_BEGIN STRING_BEGIN "x" STRING_END GETITEM_END
F_EXPR_END
F_STRING_BEGIN " " "d" "e" "f" F_STRING_END

F_END

where f-literals are defined as F_START + F_STRING + (F_EXPR + F_STRING)* + F_END

all of this of course accounting for different delimiters and so on

i consider this important enough to defer f-literals to 3.7 if it can’t get in in time.

I just wanted to let you know, Philipp, that your email comes off as somewhat demanding, e.g. "I want this changed". Had you asked why the decision was made then your email would not come off as "I'm right and you're wrong" and more about you asking for clarification to understand why, and then if you still disagreed with the thought process then bring up that you think it may have been a mistake.

sorry. i just wanted to make my feelings clear since i think this is an overlooked issue and the time is tight, in hope that maybe someone is inspired to listen. i thought the PEP’s wording was hint enough to explain the rationale (convenient reuse of tokenization code)

i’ll patiently await clarification about this, and again: sorry for sounding demanding :(

-Brett

Cheers, Philipp