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

[Steven D'Aprano]

On 11/05/13 15:12, Andrew Barnert wrote:

> Why does it need to be compile time? Do people really run into cases that frequently where the cost of concatenating or dedenting strings at import time is significant?


String constants do not need to be concatenated only at import time.

Strings frequently need to be concatenated at run-time, or at function call time, or inside loops. For constants known at compile time, it is better to use a string literal rather than a string calculated at run-time for the same reason that it is better to write 2468 rather than 2000+400+60+8 -- because it better reflects the way we think about the program, not just because of the run-time expense of extra unnecessary additions/concatenations.


> If so, it seems like something more dramatic might be warranted, like allowing the compiler to assume that method calls on literals have the same effect at compile time as at runtime so it can turn them into constants.

In principle, the keyhole optimizer could make that assumption. In practice, there is a limit to how much effort people put into the optimizer. Constant-folding method calls is probably past the point of diminishing returns.



-- 
Steven