Arch Linux

Package version: python-tensorflow-cuda 1.2.1-1


Steps to reproduce:
```
[omtcyfz@omtcyfz-arch ~]$ python
Python 3.6.1 (default, Mar 27 2017, 00:27:06)
[GCC 6.3.1 20170306] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import tensorflow
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3.6/site-packages/tensorflow/__init__.py", line 24, in <module>
from tensorflow.python import *
File "/usr/lib/python3.6/site-packages/tensorflow/python/__init__.py", line 63, in <module>
from tensorflow.python.framework.framework_lib import *
File "/usr/lib/python3.6/site-packages/tensorflow/python/framework/framework_lib.py", line 100, in <module>
from tensorflow.python.framework.subscribe import subscribe
File "/usr/lib/python3.6/site-packages/tensorflow/python/framework/subscribe.py", line 26, in <module>
from tensorflow.python.ops import variables
File "/usr/lib/python3.6/site-packages/tensorflow/python/ops/variables.py", line 26, in <module>
from tensorflow.python.ops import control_flow_ops
File "/usr/lib/python3.6/site-packages/tensorflow/python/ops/control_flow_ops.py", line 70, in <module>
from tensorflow.python.ops import tensor_array_ops
File "/usr/lib/python3.6/site-packages/tensorflow/python/ops/tensor_array_ops.py", line 33, in <module>
from tensorflow.python.util import tf_should_use
File "/usr/lib/python3.6/site-packages/tensorflow/python/util/tf_should_use.py", line 28, in <module>
from backports import weakref # pylint: disable=g-bad-import-order
ModuleNotFoundError: No module named 'backports'
>>> quit()
```

Since 1.2.0 importing tensorflow produces the described error, which indicates `backports` Python package absence. I didn't find this package in Arch package index and it's certainly not in the [python-tensorflow-cuda] package requierments, but it seems like the solution would be simply installing that package along with python-tensorflow-cuda.