Add initial mypy configuration and types

As a first step, add type hints to variables whose type `mypy` cannot
infer automatically. This is the minimal set of type hints that allow
running `mypy` without any arguments, and having it not fail.

We currently ignore C extensions that mypy can't process directly.
Later, we can look into generating stubs for such modules (potentially
automatically).

1 files changed, 10 insertions, 0 deletions

diff --git a/tox.ini b/tox.ini
index 39381dc02..c1a04dda5 100644
--- a/tox.ini
+++ b/tox.ini
@@ -99,6 +99,16 @@ deps =
     -rrequirements/dev-requirements.txt
     -rrequirements/plugin-requirements.txt
 
+#
+# Running static type checkers
+#
+[testenv:mypy]
+skip_install = True
+commands =
+    mypy {posargs}
+deps =
+    mypy
+
 
 #
 # Building documentation