enable mypy on CI (#1471)

.circleci/config.yml

@@ -19,6 +19,19 @@ runtest: &runtest
 version: 2.1
 
 jobs:
+  type-check:
+    docker:
+      - image: awav/tensorflow:2.1
+
+    steps:
+      - checkout
+      - run:
+          name: Install type checker
+          command: pip install mypy
+      - run:
+          name: Run type checker
+          command: mypy .
+
   unit-test:
     <<: *runtest
     docker:
@@ -103,6 +116,10 @@ workflows:
   version: 2.1
   build_test_and_deploy:
     jobs:
+      - type-check:
+          filters:
+            tags:
+              only: /^v[0-9]+(\.[0-9]+)*(-rc[0-9]+)?/
       - format-checker:
           filters:
             tags:

Makefile

@@ -23,5 +23,8 @@ package:
 format:
 	black -t py36 -l 100 gpflow tests doc setup.py
 
+type-check:
+    mypy .
+
 test:
 	pytest -v --durations=10 tests/

gpflow/base.py

@@ -107,7 +107,7 @@ def __init__(
 
         self._transform = transform
         self.prior = prior
-        self.prior_on = prior_on
+        self.prior_on = prior_on  # type: ignore  # see https://github.com/python/mypy/issues/3004
 
         if isinstance(value, tf.Variable):
             self._unconstrained = value

mypy.ini

@@ -1,2 +1,19 @@
 [mypy]
 ignore_missing_imports = True
+
+; the following modules are not passing mypy, so we're skipping them until they've been fixed up.
+; see github issue https://github.com/GPflow/GPflow/issues/1368 for more information. Note that some
+; modules that haven't had types added are passing anyway so may not appear below.
+;
+; remove modules from this skip list when types have been added
+[mypy-gpflow.conditionals.*,gpflow.config.*,gpflow.covariances.*,gpflow.expectations.*]
+ignore_errors = True
+
+[mypy-gpflow.kernels.*,gpflow.models.*,gpflow.monitor.*,gpflow.optimizers.*,gpflow.utilities.*]
+ignore_errors = True
+
+[mypy-gpflow.mean_functions]
+ignore_errors = True
+
+[mypy-tests.*]
+ignore_errors = True

tests_requirements.txt

@@ -1,3 +1,4 @@
+mypy
 black
 pytest>=3.5.0
 pytest-random-order