[Python-ideas] Break multiple loop levels

[David Mertz]

To be clear in this thread, I don't think I'm really ADVOCATING for a
multi-level break.  My comments are simply noting that I personally fairly
often encounter the situation where they would be useful.  At the same
time, I worry about Python gaining sometimes-useful features that
complicate the overall language and bring it closer to Perl's "everyone can
write in their own style."

So to answer Chris' question... well, i did find something recent, but it
has a ton of other extraneous stuff.  But I've simplified to something that
isn't that much different from my example from my tablet yesterday, but is
fairly realistic still.

I have an existing function that looks roughly like this:

def find_needle_in_haystacks():
    found_needle = False
    for haystack in glob.glob('path/to/stuff/*'):
        fh = open(fname)
        header = fh.readline()
        if get_format(header) == 'foo':
            for line in fh:
                status = process_foo(line)
                if status = -1:
                    found_needle = True
                    break
        elif get_format(header) == 'bar':
            for line in fh:
                status = process_bar(line)
                if status = -1:
                    found_needle = True
                    break

        if found_needle:
            break

If I had a "labelled break" feature, I might rewrite it something like the
following (picking convenient syntax that I'm not per-se advocating as
best, even if the concept is adopted):

# Hypothetical future labelled break:
def find_needle_in_haystacks():
    for haystack in glob.glob('path/to/stuff/*') label HAYSTACKS:
        fh = open(fname)
        header = fh.readline()
        if get_format(header) == 'foo':
            for line in fh:
                if process_foo(line) == -1:
                    break HAYSTACKS
        elif get_format(header) == 'bar':
            for line in fh:
                if process_bar(line) == -1:
                    break HAYSTACKS

In any case, it's often possible to either (a) redefine the inner loop
>> as some sort of container operation, or (b) redefine the outer
>> operation as a function, and use "return". So it would be helpful to
>> have an example that CAN'T be rewritten in one of those ways, to use
>> as a compelling example.
>>
>
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