That would require changes to all existing static analysis tools (again).
On Thu, Sep 17, 2020 at 8:31 PM Dennis Sweeney <[email protected]>
wrote:
> I was definitely not proposing "spooky action at a distance". My proposal
> is to existing f-strings as the `__setattr__` protocol is to the
> `__getattr__` protocol. The template would only ever be hard-coded inline
> during the f-string assignment. This is the same restriction that existing
> f-strings have. I am suggesting a syntactic construct where f-strings can
> be assignment targets, not suggesting to keep track of which strings were
> f-strings or overriding assignment or something silly like that.
>
> Existing f-strings do not aim to replace str.format in situations where
> the format string is re-used.
> Likewise, the proposal would not aim to replace regular expression in
> situations where the pattern is re-used.
>
> The change would amount a syntax change for assignments: whenever an
> f-string is on the LHS of an assignment, the interpreter would do a parsing
> operation, and there would be no change to code where the f-string is in
> any other situation. This is again analogous to the behavior of
> `__getattr__` and `__setattr__`.
>
> For example,
>
> f"""<a href="{url}">{text}</a>""" = html
>
> Would be roughly equivalent to
>
> url, text = re.fullmatch(r"""<a href="(.*)">(.*)</a>""", html).groups()
>
Would this ever raise an exception on assignment?
The shortest match / greedy/non-greedy aspect of this is something that
regex is designed to handle.
>>> (a, b, c) = 1, 2
<<< ValueError: not enough values to unpack (expected 3, got 2)
>
> The LHS is never evaluated, it's only assigned to.
>
Why aren't either of these syntaxes for setting local variables supported?
locals().update(**kwargs)
locals()['url'] = '...'
Maybe it's just that every existing linter will complain about test
assertions that reference local variables that are only defined in an
f-string,
and I assume that f'{str:d{2}}' (r'(?P<str>\d{2})') doesn't work without
extending the f-string grammar,
but I also cringe at this syntax.
I also prefer the way that re, regex, and parse return a dict and don't
overload assignment for parser evaluation or variable allocation and
initialization)
(Though I do find myself reaching for the more advanced destructuring
assignment features of ECMAscript
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment
)
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