Collecting backports.weakref==1.0.post1
  1 location(s) to search for versions of backports.weakref:
  * https://pypi.python.org/simple/backports-weakref/
  Getting page https://pypi.python.org/simple/backports-weakref/
  Analyzing links from page https://pypi.python.org/simple/backports-weakref/
    Found link https://pypi.python.org/packages/12/ab/cf35cf43a4a6215e3255cf2e49c77d5ba1e9c733af2aa3ec1ca9c4d02592/backports.weakref-1.0.post1.tar.gz#md5=96ae6adc9b299b1f58849b3b1f8577d7 (from https://pypi.python.org/simple/backports-weakref/), version: 1.0.post1
    Found link https://pypi.python.org/packages/6a/f7/ae34b6818b603e264f26fe7db2bd07850ce331ce2fde74b266d61f4a2d87/backports.weakref-1.0rc1-py3-none-any.whl#md5=e314990c6b6fe1cffc8c120ed3b66b44 (from https://pypi.python.org/simple/backports-weakref/), version: 1.0rc1
    Found link https://pypi.python.org/packages/88/ec/f598b633c3d5ffe267aaada57d961c94fdfa183c5c3ebda2b6d151943db6/backports.weakref-1.0.post1-py2.py3-none-any.whl#md5=a0264576cb0ded29ccfe620fa0db6e94 (from https://pypi.python.org/simple/backports-weakref/), version: 1.0.post1
    Found link https://pypi.python.org/packages/bc/cc/3cdb0a02e7e96f6c70bd971bc8a90b8463fda83e264fa9c5c1c98ceabd81/backports.weakref-1.0rc1.tar.gz#md5=c3dcb466fe3bbd72b6af87c0fa547f24 (from https://pypi.python.org/simple/backports-weakref/), version: 1.0rc1
    Skipping link https://pypi.python.org/packages/d1/08/ddb4e629e1dc5c651343afe311a157999ac1a1e941e1f955959706a00309/backports.weakref-1.0rc1-py2-none-any.whl#md5=406220a08eeee823a993a5ea80910a53 (from https://pypi.python.org/simple/backports-weakref/); it is not compatible with this Python
  Using version 1.0.post1 (newest of versions: 1.0.post1)
  Downloading backports.weakref-1.0.post1-py2.py3-none-any.whl
  Downloading from URL https://pypi.python.org/packages/88/ec/f598b633c3d5ffe267aaada57d961c94fdfa183c5c3ebda2b6d151943db6/backports.weakref-1.0.post1-py2.py3-none-any.whl#md5=a0264576cb0ded29ccfe620fa0db6e94 (from https://pypi.python.org/simple/backports-weakref/)
  Saved /tmp/tmpgsnoh1to/backports.weakref-1.0.post1-py2.py3-none-any.whl
Skipping backports.weakref, due to already being wheel.
Cleaning up...
  Removing source in /tmp/pip-build-ev41mm1n/backports.weakref