On 2015-08-10 20:23, Guido van Rossum wrote:
On Mon, Aug 10, 2015 at 8:49 PM, Eric V. Smith <e...@trueblade.com
<mailto:e...@trueblade.com>> wrote:
On 08/10/2015 02:44 PM, Yury Selivanov wrote:
> On 2015-08-10 2:37 PM, Eric V. Smith wrote:
>> This is why I think PEP-498 isn't the solution for i18n. I'd really like
>> to be able to say, in a debugging context:
>>
>> print('a:{self.a} b:{self.b} c:{self.c} d:{self.d}')
>>
>> without having to create locals to hold these 4 values.
>
> Why can't we restrict expressions in f-strings to
> attribute/item getters?
>
> I.e. allow f'{foo.bar.baz}' and f'{self.foo["bar"]}' but
> disallow f'{foo.bar(baz=something)}'
It's possible. But my point is that Barry doesn't even want
attribute/item getters for an i18n solution, and I'm not willing to
restrict it that much.
I also don't want to tie this closely to i18n. That is (still) very much
a wold of its own.
What I want with f-strings (by any name) is a way to generalize from
print() calls with multiple arguments. We can write
print('Todo:', len(self.todo), '; busy:', len(self.busy))
but the same thing is more awkward when you have to pass it as a single
string to a function that just sends one string somewhere. And note that
the above example inserts a space before the ';' which I don't really
like. So it would be nice if instead we could write
print(f'Todo: {len(self.todo)}; busy: {len(self.busy)}')
which IMO is just as readable as the multi-arg print() call[1], and
generalizes to other functions besides print().
In fact, the latter form has less punctuation noise than the former --
every time you insert an expression in a print() call, you have a
quote+comma before it and a comma+quote after it, compared to a brace
before and one after in the new form. (Note that this is an argument for
using f'{...}' rather than '\{...}' -- for a single interpolation it's
the same amount of typing, but for multiple interpolations,
f'{...}{...}' is actually shorter than '\{...}\{...}', and also the \{
part is ugly.)
Anyway, this generalization from print() is why I want arbitrary
expressions. Wouldn't it be silly if we introduced print() today and
said "we don't really like to encourage printing complicated
expressions, but maybe we can introduce them in a future version"... :-)
Continuing the print()-generalization theme, if things become too long
to fit on a line we can write
print('Todo:', len(self.todo),
'; busy:', len(self.busy))
Can we allow the same in f-strings? E.g.
print(f'Todo: {len(self.todo)
}; busy: {len(self.busy)
}')
or is that too ugly? It could also be solved using implicit
concatenation, e.g.
print(f'Todo: {len(self.todo)}; '
f'busy: {len(self.busy)}')
[1] Assuming syntax colorizers catch on.
I'd expect f'...' to follow similar rules to '...'.
You could escape it:
print(f'Todo: {len(self.todo)\
}; busy: {len(self.busy)\
}')
which would be equivalent to:
print(f'Todo: {len(self.todo) }; busy: {len(self.busy) }')
or use triple-quoted a f-string:
print(f'''Todo: {len(self.todo)
}; busy: {len(self.busy)
}''')
which would be equivalent to:
print(f'Todo: {len(self.todo)\n }; busy: {len(self.busy)\n }')
(I think it might be OK to have a newline in the expression because
it's wrapped in {...}.)
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