invalid_id_arr=["id123-3431","id124-4341","id125-4341","id126-1w","id789-123","id666"]
valid_id_arr=["id123-12345","id124-1122","id125-13232","id126-12332","id1new","idagain"]
valid_id_set = set(ele.split('-')[0] for ele in valid_id_arr)
diff = [ele for ele in invalid_id_arr if ele.split('-')[0] not in valid_id_set]
print diff
aW52YWxpZF9pZF9hcnI9WyJpZDEyMy0zNDMxIiwiaWQxMjQtNDM0MSIsImlkMTI1LTQzNDEiLCJpZDEyNi0xdyIsImlkNzg5LTEyMyIsImlkNjY2Il0gCnZhbGlkX2lkX2Fycj1bImlkMTIzLTEyMzQ1IiwiaWQxMjQtMTEyMiIsImlkMTI1LTEzMjMyIiwiaWQxMjYtMTIzMzIiLCJpZDFuZXciLCJpZGFnYWluIl0KdmFsaWRfaWRfc2V0ID0gc2V0KGVsZS5zcGxpdCgnLScpWzBdIGZvciBlbGUgaW4gdmFsaWRfaWRfYXJyKQpkaWZmID0gW2VsZSBmb3IgZWxlIGluIGludmFsaWRfaWRfYXJyIGlmIGVsZS5zcGxpdCgnLScpWzBdIG5vdCBpbiB2YWxpZF9pZF9zZXRdCnByaW50IGRpZmY=