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In your code, by replacing [] by () and range() by xrange(), you build a generator, that will loop in real time, without storing all values in a list:

sage: A = ((a,b,c,d) for a in xrange(100) for b in xrange (100) for c in xrange (100) for d in xrange (100))

sage: A
<generator object <genexpr> at 0x5d269b0>

sage: for f in A:
....:     print f
(0, 0, 0, 0)
(0, 0, 0, 1)
(0, 0, 0, 2)
(0, 0, 0, 3)
(0, 0, 0, 4)
...

In your code, by just replacing [] by () and range() by xrange(), you build a generator, that will loop in real time, without storing all values in a list:list, saving a lot of memory:

sage: A = ((a,b,c,d) for a in xrange(100) for b in xrange (100) for c in xrange (100) for d in xrange (100))

sage: A
<generator object <genexpr> at 0x5d269b0>

sage: for f in A:
....:     print f
(0, 0, 0, 0)
(0, 0, 0, 1)
(0, 0, 0, 2)
(0, 0, 0, 3)
(0, 0, 0, 4)
...

sage: B = cartesian_product_iterator([xrange(100) for i in range(4)])

sage: for f in B:
....:     print f
(0, 0, 0, 0)
(0, 0, 0, 1)
(0, 0, 0, 2)
(0, 0, 0, 3)
(0, 0, 0, 4)
...