[Python-Dev] PEP 498: Literal String Interpolation is ready for pronouncement (original) (raw)

Nathaniel Smith njs at pobox.com
Sat Sep 5 21:23:49 CEST 2015

On Sep 5, 2015 11:32 AM, "Eric V. Smith" <eric at trueblade.com> wrote:

> Actually, my current implementation doesn't use the lexer, although I > suppose it could. I'm currently manually scanning the string, keeping > track of strings and parens. To find the end of an expression, it looks > for a '!', ':', or non-doubled '}', not inside of a string or (), [], or > {}. There's a special case for '!=' so the bang isn't seen as ending the > expression. Ignore the part about non-doubled '}'. The actual description is: To find the end of an expression, it looks for a '!', ':', or '}', not inside of a string or (), [], or {}. There's a special case for '!=' so the bang isn't seen as ending the expression.

Sounds like you're reimplementing a lot of the lexer... I guess that's doable, but how confident are you that your definition of "inside a string" matches the original in all corner cases?

In any case the abstract language definition part should be phrased in terms of the python lexer -- the expression ends when you encounter the first } token that is not nested inside () [] {} tokens, and then you can implement it however makes sense...

(This is then the same rule that patsy uses to find the end of python expressions embedded inside patsy formula strings: patsy.readthedocs.org)

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