On Tue, Mar 1, 2022 at 2:23 PM Steven D'Aprano <[email protected]> wrote:
> try:
> do_this()
> if condition: raise MyBreak
> do_that()
> if condition: raise MyBreak
> do_next_step()
> if condition: raise MyBreak
> do_last_step()
> except MyBreak:
> pass
>
Why not:
while True:
[loop body with ordinary breaks]
break
It's less to write and almost free of charge*, and it also supports redo
(continue).
MyBreak has the advantage that you can raise it in nested loops and
subfunctions, although that could be a disadvantage since it makes the
control flow confusing.
This goes for repeat-until also: I always write it while True: ... if cond:
break. I just grepped through some personal Python projects and about 40%
of my while-loop conditions are True.
* The break at the end is free, but Python 3.10.2 inserts a NOP at the
location of the while True, and the peephole optimizers of earlier Python
versions have done other things. It looks like there's been a lot of work
on bytecode efficiency in 3.11, so maybe it will become truly free, but I
haven't checked.
3.11 has range-based exception handling (issue 40222), so the try: approach
is free if you don't raise MyBreak (but expensive if you do).
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