On Wed, Mar 01, 2017 at 10:37:17AM +0100, Wolfgang Maier wrote:
> Now here's the proposal: allow an except (or except break) clause to
> follow for/while loops that will be executed if the loop was terminated
> by a break statement.
Let me see if I understand the proposal in full. You would allow:
for i in (1, 2, 3):
print(i)
if i == 2:
break
except break: # or just except
assert i == 2
print("a break was executed")
else:
print("never reached") # this is never reached
print("for loop is done")
as an alternative to something like:
broke_out = False
for i in (1, 2, 3):
print(i)
if i == 2:
broke_out = True
break
else:
print("never reached") # this is never reached
if broke_out:
assert i == 2
print("a break was executed")
print("for loop is done")
I must admit the suggestion seems a little bit neater than having to
manage a flag myself, but on the other hand I can't remember the last
time I've needed to manage a flag like that.
And on the gripping hand, this is even simpler than both alternatives:
for i in (1, 2, 3):
print(i)
if i == 2:
assert i == 2
print("a break was executed")
break
else:
print("never reached") # this is never reached
print("for loop is done")
There are some significant unanswered questions:
- Does it matter which order the for...except...else are in?
Obviously the for block must come first, but apart from that?
- How is this implemented? Currently "break" is a simple
unconditional GOTO which jumps past the for block. This will
need to change to something significantly more complex.
- There are other ways to exit a for-loop than just break. Which
of them, if any, will also run the except block?
--
Steve
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