On 20/07/2020 09:56, Alex Hall wrote:
On Mon, Jul 20, 2020 at 10:36 AM Rob Cliffe via Python-ideas
<python-ideas@python.org <mailto:python-ideas@python.org>> wrote:
May I repeat: Spelling 'if break:' and 'if not break:' rather
than say
'on_break:' etc. would avoid adding new keywords.
I don't know what to do about the zero iterations case, though.
It could be that if `break` appears somewhere that an expression is
expected, it becomes an expression with the value 0 or 1 (or False or
True) to indicate the number of breaks that happened in the previous
loop, and similarly some other bit of code involving keywords can
become the number of iterations of the previous loop. This could be
represented by `for`, `len(for)`, `pass`, etc. So one might write:
```
for x in ...:
...
if not pass:
...
elif pass == 1:
...
else:
...
```
`break' becoming an expression is fine by me.
But detecting the number of iterations (however it's spelt) might be tricky.
Always counting the number of iterations would slow down *every*
for/while loop - surely unacceptable.
So the compilation process must only incorporate this loop-counting when
the loop is followed (after 100 lines of code??) by a reference to the
loop count.
Another way would be for the first iteration (i.e. the first call of
`next') to be coded separately (in the bytecode). If the first call
does not raise StopIteration, it could set a flag meaning "at least 1
iteration occurred", But this would bloat the code, and again doesn't
seem like a great idea if it applies to *every* for/while loop.
Therefore: I suggest that the proposal should be modified to just detect
break or no break. That's already progress. And if in future someone
thinks of a brilliant way of detecting zero (or N) iterations, that can
be added later.
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