py-graph-tool uses incorrect (default) python version 2.7, propagates to dependencies

[ssllmit (ss)]

py-graph-tool uses the incorrect python version, default to v. 2.7 in its port file, which results in incorrect dependencies during the build.

First, clean everything and set python to use v. 3.6:

sudo port clean --all py-graph-tool, 
sudo port select --set python python36
hash -r

Confirm:

$ python --version
Python 3.6.7

But the correct python version dependency doesn't propagate:

$ port list depof:py-graph-tool
py27-graph-tool                @2.27           python/py-graph-tool

This results in boost being compiled and installed with an incorrect python version:

$ sudo port -pN install py-graph-tool
--->  Computing dependencies for py-graph-tool
--->  Dependencies to be installed: py27-graph-tool boost cgal
--->  Fetching archive for boost
--->  Attempting to fetch boost-1.66.0_3+no_single+no_static+python27.darwin_17.x86_64.tbz2 from https://packages.macports.org/boost

Even an install with an explicit python version (v. 3.6) gets the wrong python version (default v. 2.7):

sudo port -pN install py36-graph-tool
--->  Computing dependencies for py36-graph-tool
--->  Dependencies to be installed: boost cgal
--->  Fetching archive for boost
--->  Attempting to fetch boost-1.66.0_3+no_single+no_static+python27.darwin_17.x86_64.tbz2 from https://packages.macports.org/boost

This issue appears to go beyond py-graph-tool because boost also shows the same dependency issue:

port list depof:boost
bzip2                          @1.0.6          archivers/bzip2
expat                          @2.2.6          textproc/expat
icu                            @58.2           devel/icu
libiconv                       @1.15           textproc/libiconv
python27                       @2.7.15         lang/python27
zlib                           @1.2.11         archivers/zlib

Admittedly, this may be a problem with my configuration, but I did my due diligence and cannot identify any local problems.

FWIW, I'm trying to track down a segmentation fault with gt.graph_draw that I hope is related to this build problem…

gt.graph_draw(g)
Segmentation fault: 11