1.15.72 has been released, and it supports PyYAML 3.13 (~amd64 ATM) since 1.5.56. https://pypi.python.org/pypi/awscli https://github.com/aws/aws-cli/blob/1.15.56/requirements.txt#L14
Also Python 3.7 is now supported
WARNING: One or more updates/rebuilds have been skipped due to a dependency conflict: dev-python/pyyaml:0 (dev-python/pyyaml-3.13:0/0::gentoo, ebuild scheduled for merge) conflicts with <=dev-python/pyyaml-3.12[python_targets_python2_7(-),python_targets_python3_6(-),-python_single_target_python2_7(-),-python_single_target_python3_4(-),-python_single_target_python3_5(-),-python_single_target_python3_6(-)] required by (dev-python/awscli-1.15.10:0/0::gentoo, installed) ^^ ^^^^
Also `colorama` dependency should be bumped to ~0.3.9 (or =<0.3.10) for Python 3.7 support
New awscli is in repository. No Py3.7 support because not all dependencies support Py3.7 yet.