Do this with some cython tricks and some caching of type attributes.
Cython 0.28 compiles this code to be quite a bit faster than Cython
0.27 does (the below uses 0.28), but it's still a win on both.

The type caching could potentially be a compatibility issue, but in
practice I suspect it won't be.

Benchmarks on 3.6:

+--------------------+------------------+-----------------------------+
| Benchmark          | 3.6              | 3.6 This Branch             |
+====================+==================+=============================+
| getattr gevent     | 190 ns           | 158 ns: 1.20x faster (-17%) |
+--------------------+------------------+-----------------------------+
| setattr gevent     | 180 ns           | 165 ns: 1.09x faster (-8%)  |
+--------------------+------------------+-----------------------------+
| getattr gevent sub | 540 ns           | 175 ns: 3.09x faster (-68%) |
+--------------------+------------------+-----------------------------+
| setattr gevent sub | 528 ns           | 179 ns: 2.95x faster (-66%) |
+--------------------+------------------+-----------------------------+
| setattr native     | 80.8 ns          | 78.8 ns: 1.03x faster (-2%) |
+--------------------+------------------+-----------------------------+

Not significant (3): getattr native; getattr native sub; setattr native sub

Benchmarks on 2.7:

+--------------------+------------------+-----------------------------+
| Benchmark          | local_27_master2 | local_27_tweak2             |
+====================+==================+=============================+
| getattr gevent     | 162 ns           | 158 ns: 1.03x faster (-3%)  |
+--------------------+------------------+-----------------------------+
| setattr gevent     | 173 ns           | 165 ns: 1.04x faster (-4%)  |
+--------------------+------------------+-----------------------------+
| getattr gevent sub | 471 ns           | 181 ns: 2.61x faster (-62%) |
+--------------------+------------------+-----------------------------+
| setattr gevent sub | 462 ns           | 190 ns: 2.44x faster (-59%) |
+--------------------+------------------+-----------------------------+
| getattr native     | 87.4 ns          | 89.7 ns: 1.03x slower (+3%) |
+--------------------+------------------+-----------------------------+
| setattr native     | 133 ns           | 110 ns: 1.20x faster (-17%) |
+--------------------+------------------+-----------------------------+
| getattr native sub | 101 ns           | 97.9 ns: 1.03x faster (-3%) |
+--------------------+------------------+-----------------------------+
| setattr native sub | 118 ns           | 111 ns: 1.06x faster (-6%)  |
+--------------------+------------------+-----------------------------+

PyPy unfortunately shows as a little slower, though I'm not sure I
fully believe that:

+--------------------+-------------------+-----------------------------+
| Benchmark          | local_pypy_master | local_pypy_tweak2           |
+====================+===================+=============================+
| getattr gevent     | 135 ns            | 157 ns: 1.16x slower (+16%) |
+--------------------+-------------------+-----------------------------+
| setattr gevent     | 126 ns            | 162 ns: 1.28x slower (+28%) |
+--------------------+-------------------+-----------------------------+
| getattr gevent sub | 150 ns            | 175 ns: 1.17x slower (+17%) |
+--------------------+-------------------+-----------------------------+
| setattr gevent sub | 153 ns            | 183 ns: 1.20x slower (+20%) |
+--------------------+-------------------+-----------------------------+
| getattr native     | 0.18 ns           | 0.19 ns: 1.05x slower (+5%) |
+--------------------+-------------------+-----------------------------+
| setattr native     | 0.18 ns           | 0.20 ns: 1.06x slower (+6%) |
+--------------------+-------------------+-----------------------------+
| getattr native sub | 0.18 ns           | 0.19 ns: 1.05x slower (+5%) |
+--------------------+-------------------+-----------------------------+
| setattr native sub | 0.19 ns           | 0.18 ns: 1.06x faster (-6%) |
+--------------------+-------------------+-----------------------------+