import re
p = re.compile(r'(\[[^\[\]]*\[.*?\][^\]\[]*\])', re.MULTILINE)
test_str = "[[1,2,3],[3,5,3],[9,8,9]] aoeu [5,6,9] aoeu [[4,5,5]] [[1,2,3],[3,5,3],3]\n[[1,2,3],4,[3,5,3],3]\n[1,2,3,[3,5,3],3]\n[1,2]"
print(re.findall(p, test_str))
aW1wb3J0IHJlCnAgPSByZS5jb21waWxlKHInKFxbW15cW1xdXSpcWy4qP1xdW15cXVxbXSpcXSknLCByZS5NVUxUSUxJTkUpCnRlc3Rfc3RyID0gIltbMSwyLDNdLFszLDUsM10sWzksOCw5XV0gYW9ldSBbNSw2LDldIGFvZXUgW1s0LDUsNV1dIFtbMSwyLDNdLFszLDUsM10sM11cbltbMSwyLDNdLDQsWzMsNSwzXSwzXVxuWzEsMiwzLFszLDUsM10sM11cblsxLDJdIgogCnByaW50KHJlLmZpbmRhbGwocCwgdGVzdF9zdHIpKQ==
['[[1,2,3],[3,5,3],[9,8,9]]', '[[4,5,5]]', '[[1,2,3],[3,5,3],3]', '[[1,2,3],4,[3,5,3],3]', '[1,2,3,[3,5,3],3]']