[Python-ideas] Implicit string literal concatenation considered harmful?

[MRAB]

On 16/05/2013 08:08, Serhiy Storchaka wrote:
> 10.05.13 21:48, Guido van Rossum написав(ла):
>> I just spent a few minutes staring at a bug caused by a missing comma
>> -- I got a mysterious argument count error because instead of foo('a',
>> 'b') I had written foo('a' 'b').
>>
>> This is a fairly common mistake, and IIRC at Google we even had a lint
>> rule against this (there was also a Python dialect used for some
>> specific purpose where this was explicitly forbidden).
>>
>> Now, with modern compiler technology, we can (and in fact do) evaluate
>> compile-time string literal concatenation with the '+' operator, so
>> there's really no reason to support 'a' 'b' any more. (The reason was
>> always rather flimsy; I copied it from C but the reason why it's
>> needed there doesn't really apply to Python, as it is mostly useful
>> inside macros.)
>
> As was said before the '+' operator has less priority than the '%'
> operator and an attribute access, i.e. it requires parenthesis in some
> cases. However parenthesis introduce a noise and can cause other types
> of errors.
>
[snip]
I wonder whether we could use ".". Or would that be too confusing?

> In all cases only multiline implicit string literal concatenation cause
> problem. What if forbid implicit string literal concatenation only
> between string literals on different physical lines? A deliberate string
> literal concatenation can be made with explicit line joining.
>
>           raise ValueError('Type names and field names must be valid '\
>                            'identifiers: %r' % name)
>
           raise ValueError('Type names and field names must be valid ' .
                            'identifiers: %r' % name)
>
>           raise ValueError('{} not bottom-level directory in '\
>                            '{!r}'.format(_PYCACHE, path))
>
           raise ValueError('{} not bottom-level directory in ' .
                            '{!r}'.format(_PYCACHE, path))