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Sat Sep 5 21:23:49 CEST 2015 · https://mail.python.org/pipermail/python-dev/2015-September/141472.html

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)

-n
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