add black and mypy to dev requirements for cpython > 3.5

psf/black#727
python/typed_ast#111

Author: Greg Guthe

requirements-dev.txt

@@ -17,3 +17,9 @@ wheel
 
 # Requirements for updating the vendored html5lib
 hashin
+
+# Requirements for format-check most recently black==20.8b1
+black; implementation_name == "cpython" and python_version > "3.5"
+
+# Requirements for type-check most recently mypy==0.790 and mypy-extensions==0.4.3
+mypy; implementation_name == "cpython" and python_version > "3.5"

tox.ini

@@ -61,7 +61,6 @@ basepython = python3.8
 changedir = scripts
 deps =
     -rrequirements-dev.txt
-    black
 commands =
     ./run_tests.sh format-check