Access _struct attributes directly instead of mucking with getattr.
Access _struct attributes directly instead of mucking with getattr.

string_reverse():  Simplify.

assertRaises():  Raise TestFailed on failure.

test_unpack_from(), test_pack_into(), test_pack_into_fn():  never
use `assert` to test for an expected result (it doesn't test anything
when Python is run with -O).

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator