Well, its still not installing for 3.6. Although make clean shows cleaning for both 2.7 and 3.6, installation always goes for 2.7 (even make config), which is already installed.
make showconfigand the error message you get.
root@water:/usr/ports/math/py-matplotlib # make showconfig ===> The following configuration options are available for py27-matplotlib-1.5.3_3: EXAMPLES=off: Build and/or install examples GTKAGGBACKEND=off: GTKAgg backend support GTKBACKEND=off: GTK backend support QT4AGGBACKEND=off: Qt4Agg backend support QT5AGGBACKEND=off: Qt5Agg backend support TKAGGBACKEND=off: TKAgg backend support WXAGGBACKEND=off: WXAgg backend support ===> Use 'make config' to modify these settings
root@water:/usr/ports/math/py-matplotlib # make clean ===> Cleaning for py27-matplotlib-1.5.3_3 ===> Cleaning for py36-matplotlib-1.5.3_3
make showconfigoutput looks good. You can run
make FLAVOR=py36 installto install the Python 3.6 version like with numpy earlier.
make FLAVOR=py36 install BATCH="yes"
Installing py36-sip-4.19.2,1... pkg-static: py36-sip-4.19.2,1 conflicts with py27-sip-4.19.2,1 (installs files into the same place). Problematic file: /usr/local/bin/sip *** Error code 70 Stop. make: stopped in /usr/ports/devel/py-sip *** Error code 1 Stop. make: stopped in /usr/ports/devel/py-qt5-core *** Error code 1 Stop. make: stopped in /usr/ports/devel/py-qt5