Add mypy to CI and create code style guidelines

.circleci/config.yml

@@ -13,6 +13,9 @@ jobs:
       - run:
           name: Lint code
           command: make lint
+      - run:
+          name: Static typechecking
+          command: make mypy
       - run:
           name: Run tests
           command: make test

CONTRIBUTING.md

@@ -0,0 +1,13 @@
+# Contributing Code
+
+## Style
+We follow PEP8 with the exception of maximum line length set to 120. We
+use `numpy` style docstrings with the exception of ommitting argument
+types in the docstrings in favour of type hint in function and class
+signatures. We use `mypy` to typecheck code with exceptions for
+libraries with missing stubs specified in `setup.cfg`.
+
+## Pull requests
+Before a PR is accepted, CircleCI builds must pass. We use `flake8` for
+linting (with exceptions to PEP8 described in `setup.cfg` and `pytest`
+for testing. We use `sphinx` for building documentation.

Makefile

@@ -9,3 +9,7 @@ test:
 .PHONY: lint
 lint:
 	flake8 .
+
+.PHONY: mypy
+mypy:
+	mypy .

requirements.txt

@@ -1,4 +1,5 @@
 pytest==4.2.0
 pytest-cov==2.6.1
 sphinx==1.8.4
-flake8==3.7.7
+flake8==3.7.7
+mypy==0.670

setup.cfg

@@ -14,3 +14,21 @@ exclude =
     doc/source/conf.py
     # post-test
     .eggs/
+
+[mypy-setuptools.*]
+ignore_missing_imports = True
+
+[mypy-numpy.*]
+ignore_missing_imports = True
+
+[mypy-pandas.*]
+ignore_missing_imports = True
+
+[mypy-sklearn.*]
+ignore_missing_imports = True
+
+[mypy-matplotlib.*]
+ignore_missing_imports = True
+
+[mypy-scipy.*]
+ignore_missing_imports = True