On Jul 22, 2015 10:31 PM, "Steven D'Aprano" <steve@pearwood.info> wrote:
[...]
I would go further and allow all the f prefixes apart from the first to be optional. To put it another way, the first f prefix "infects" all the other string fragments:
msg = (f'a long message here blah blah {x}' ' and {y} and {z} and more {stuff} and {things}' ' and perhaps even more {poppycock}' )
should be exactly the same as the first version. My reasoning is that the implicit concatenation always occurs first, so by the time the format(...) magic occurs at run-time, the interpreter no long knows which braces came from an f-string and which came from a regular string.
(Implicit concatenation is a compile-time operation, the format(...) stuff is run-time, so there is a clear and logical order of operations.)
To avoid potential surprises, I would disallow the case where the f prefix doesn't occur in the first fragment, or at least raise a compile-time warning:
'spam' 'eggs' f'{cheese}'
should raise or warn. (That restriction could be removed in the future, if it turns out not to be a problem.)
And merging f-strings: f'{foo}' f'{bar'} similarly just becomes concatenating the results of some function calls.
That's safe to do at compile-time:
f'{foo}' f'{bar}' f'{foo}{bar}'
will always be the same. There's no need to delay the concat until after the formats.
This makes perfect sense to me. -- C Anthony