On Wed, Oct 21, 2020 at 06:17:27AM +1100, Chris Angelico wrote:
> No; it can fail if the pattern actually rejects it. For instance, a
> pattern of "a{x}b{y}c" can match the string "a" but won't assign to y,
It won't assign to x either, if I'm understanding it correctly, since
there is nothing following the 'a' that matches. Or will x get the empty
string?
> however it can't match the string "q" because that doesn't match. This
> behaviour of leaving variables unassigned happens ONLY if there's a
> partial match.
>
> And just like with a regex, it would be easy enough to have a notation
> that demands end-of-string, and cannot match unless you reach that
> point in the pattern right as you reach the end of the string.
But you'll still get a partial match.
Using regex syntax, if you try to match "spam {x} eggs$" (i.e. the
prefix "spam", space, substring to be extracted, space, suffix "eggs",
end of string) against "spam is great" you will get the partial match
x="is".
If you're trying to match the address "{num:d} Main Street {city}$"
against "3.1415" you will get num=3. Maybe I'm missing something, but I
don't see why this is desirable behaviour.
[...]
> Well... yes. And oddly enough, developing a scanning mini-language
> inspired by the formatting language is *exactly* what this proposal
> is, and has always been.
That's incorrect.
The first post in this thread:
https://mail.python.org/archives/list/[email protected]/thread/JEGSKODAK5MCO2HHUF4555JZPZ6SKNEC/
literally describes it as f-strings as the target. There's no hint that
only a subset of f-string functionality will be accepted. Dennis says:
"you can assign a string to an f-string"
and proposes an exception:
"ValueError: f-string assignment target does not match ..."
I can't work out how to see messages in non-threaded date order on the
website, but it looks to me like the first suggestion that this might
not *literally* be f-strings comes about a dozen emails into the thread,
and from you, not Dennis.
The subject line doesn't say "Scanning mini-language inspired by
f-strings", it says that f-strings should be allowed as an assignment
target. I think that people can be forgiven for thinking that a thread
that says it is about making f-strings assignment targets is about
making f-strings assignment targets *wink*
I think we have at least six mini-languages now?
- regexes
- string interpolation with %
- template strings
- format mini-language
- f-strings
- date/time format strings
I think it would be quite an uphill battle to have a seventh built into
the language. You're welcome to write a PEP :-)
--
Steve
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