[issue10109] itertools.product with infinite iterator cause MemoryError.

[Terry J. Reedy]

Terry J. Reedy <tjreedy at udel.edu> added the comment:

A relatively simple change would be to allow the first iterable to be 'infinite', when repeat==1, by not calling tuple() on it. The reason for turning the iterables into concrete sequences is because they might not be reiterable. (cycle() does the same for the same reason.) But since the first iterable is only iterated once, this does not apply to it.

    if repeat == 1:
        pools = [args[0:1]].extend(tuple(pool) for pool in args[1:])
    else:
        pools = [tuple(pool) for pool in args] * repeat

The counter argument to this or any generalized proposal is that one can expand the product() into enough loops to avoid infinite (or very large) args. For example, the following produces '1AA', '1AB', ..., '1EE', '2AA', ... indefinitely.

naa=(''.join((str(n),)+s) for n in itertools.count(1)
     for s in itertools.product(string.ascii_uppercase[0:5], repeat=2))

RAYMOND: Do you think the doc should specify that each iterable must be finite, and that explicit loops are the alternative if not?

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue10109>
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