Co-routines

[Alan Kennedy]

thewrights at ozemail.com.au wrote:

> I want to execute these functions in
> "lock-step", so that the output looks like:
> 
>     1-1
>     2-2
>     1-2
>     2-2
>     1-3
>     2-3

Have you made a mistake in this output? Should it be this?

1-1
2-1
1-2
2-2
1-3
2-3

If yes, how about this?

#-------------------------
import itertools 

def seq(which, iterable):
    for i in iterable:
        yield "%d-%d" % (which, i)

times = [1,2,3]

seq1 = seq(1, times)
seq2 = seq(2, times)

for v1, v2 in itertools.izip(seq1, seq2):
    print v1
    print v2
#--------------------------

If you want to generalise the number of iterators, how about this?

#--------------------------
def lizip(iterables):
    iterables = map(iter, iterables)
    while True:
        result = [i.next() for i in iterables]
        yield tuple(result)

def seq(which, iterable):
    for i in iterable:
        yield "%d-%d" % (which, i)

y = [1,2,3] ; max_x = 5

iters = [seq(x, y) for x in range(1, max_x+1)]

for vertslice in lizip(iters):
    for v in vertslice:
        print v
#--------------------------

Note that these examples don't use "coroutines". Instead they use
python generators, which are classified as "semi-coroutines".

-- 
alan kennedy
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