Added py38 and py39 to tox.ini for newer distros

Package pandas that doens't build with py39 yet.
Packages numpy==1.19.2 and Cython==0.29.21 fails to build with py39.
Can fix with:
  Cython<0.29.21,>=0.29.13
  numpy<=1.19.2,>=1.16.4
  numexpr<=2.7.1,>=2.6.9
  pandas<=1.1.2,>=0.24.2 ; python_version < '3.9'

docs/changes.rst

@@ -4,6 +4,9 @@ Changes
 Version 1.6.6
 -------------
 
+* Added python version 3.8 and 3.9 to tox.ini for using in newer distros.
+  By :user:`juarezr`, :issue:`517`.
+
 * fix compatibility with python3.8 in `petl.timings.clock()`.
   By :user:`juarezr`, :issue:`484`.
 

setup.py

@@ -45,6 +45,7 @@
                  'Programming Language :: Python :: 3',
                  'Programming Language :: Python :: 3.6',
                  'Programming Language :: Python :: 3.7',
+                 'Programming Language :: Python :: 3.8',
                  'Topic :: Software Development :: Libraries :: Python Modules'
                  ]
 )

tox.ini

@@ -4,7 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = py27, py36, py37, py37-docs
+envlist = py27, py36, py37, py38, py39, {py37,py38,py39}-docs
 # trick to enable pre-installation of numpy and numexpr
 indexserver =
     preinstall1 = https://pypi.org/simple
@@ -15,9 +15,9 @@ indexserver =
 setenv =
     PYTHONHASHSEED = 42
     py27: PY_MAJOR_VERSION = py2
-    py36,py37: PY_MAJOR_VERSION = py3
+    py36,py37,py38,py39: PY_MAJOR_VERSION = py3
 commands =
-    py27,py36: nosetests -v petl --with-coverage --cover-package=petl
+    py27,py36,py38,py39: nosetests -v petl --with-coverage --cover-package=petl
     py37: nosetests -v --with-coverage --cover-package=petl --with-doctest --doctest-options=+NORMALIZE_WHITESPACE petl -I"csv_py2\.py" -I"db\.py"
     coverage report -m
 deps =
@@ -27,7 +27,7 @@ deps =
     -rtest_requirements.txt
     -roptional_requirements.txt
 
-[testenv:py37-docs]
+[testenv:{py37,py38,py39}-docs]
 # build documentation under similar environment to readthedocs
 changedir = docs
 deps =