tox += CPython3.9

Debian testing recently switched default python3 to be python3.9.
Let's make sure pygolang works with that python version.
Currently some tests fail - this will be addressed in the next patch.

/reviewed-on !13

setup.py

@@ -327,6 +327,7 @@ setup(
         Programming Language :: Python :: 3.6
         Programming Language :: Python :: 3.7
         Programming Language :: Python :: 3.8
+        Programming Language :: Python :: 3.9
         Programming Language :: Python :: Implementation :: CPython
         Programming Language :: Python :: Implementation :: PyPy
         Topic :: Software Development :: Interpreters

tox.ini

 [tox]
 envlist =
-    {py27d,py27,py37,py38d,py38,pypy,pypy3}-{thread,gevent}
+    {py27d,py27,py37,py38d,py38,py39d,py39,pypy,pypy3}-{thread,gevent}
 
 
 # ThreadSanitizer
@@ -10,18 +10,18 @@ envlist =
 # (*) PyPy locks its GIL (see RPyGilAcquire) by manually doing atomic cmpxchg
 # and other games, which TSAN cannot see if PyPy itself was not compiled with
 # -fsanitize=thread.
-    {py27d,py27,py37,py38d,py38           }-{thread       }-tsan
+    {py27d,py27,py37,py38d,py38,py39d,py39           }-{thread       }-tsan
 # XXX py*-gevent-tsan would be nice to have, but at present TSAN is not
 # effective with gevent, because it does not understand greenlet "thread"
 # switching and so perceives the program as having only one thread where races
 # are impossible. Disabled to save time.
-#   {py27d,py27,py37,py38d,py38           }-{       gevent}-tsan
+#   {py27d,py27,py37,py38d,py38,py39d,py39           }-{       gevent}-tsan
 
 
 # AddressSanitizer
 
 # XXX asan does not work with gevent: https://github.com/python-greenlet/greenlet/issues/113
-    {py27d,py27,py37,py38d,py38,pypy,pypy3}-{thread       }-asan
+    {py27d,py27,py37,py38d,py38,py39d,py39,pypy,pypy3}-{thread       }-asan
 
 [testenv]
 basepython =
@@ -30,6 +30,8 @@ basepython =
     py37:   python3.7
     py38d:  python3.8-dbg
     py38:   python3.8
+    py39d:  python3.9-dbg
+    py39:   python3.9
     pypy:   pypy
     pypy3:  pypy3