keep = "1 2 3 4 5 6 7 8 9 0".split();
a = "adfh23aks4j5dh234fe3412uiw1\n!";
# lazy filter
new_a = "".join(ch for ch in a if ch in keep);
keep = "1 2 3 4 5 6 7 8 9 0".split();
a = "adfh23aks4j5dh234fe3412uiw1\n!";
# lazy filter
new_a = "".join(ch for ch in a if ch in keep);