Python's itertools product memory consumption

Question

The documentation says that the cartesian product function

the actual implementation does not build up intermediate results in memory.

How can

Answer 1

Looking at the module's source code, itertools.product() actually converts every argument to a tuple:

// product_new() in itertoolsmodule.c
for (i=0; i < nargs ; ++i) {
    PyObject *item = PyTuple_GET_ITEM(args, i);
    PyObject *pool = PySequence_Tuple(item); //<==== Call tuple(arg)
    if (pool == NULL)
        goto error;
    PyTuple_SET_ITEM(pools, i, pool);
    indices[i] = 0;
}

In other words, itertools.product()'s memory consumption appears to be linear in the size of the input arguments.