Introduce automatic code formatting/linting

Code formatting makes sure that the python code looks decent, but it
does not check for coding errors.
https://black.readthedocs.io/en/stable/

Code linting runs static error detection on the python code, but does
not bother about formatting: https://pylint.readthedocs.io/en/latest/

Makefile

@@ -7,9 +7,20 @@ compile-requirements: ## Compile requirements files
 	pip-compile -o requirements/dev.txt requirements/dev.in
 	pip-compile -o requirements/docs.txt requirements/docs.in
 
-test: ## Run unit tests
+test: test-lint test-unit test-format ## Run all tests by decreasing order or priority
+
+test-format: ## Run code formatting tests
+	black --check --diff tutor
+
+test-lint: ## Run code linting tests
+	pylint --errors-only tutor
+
+test-unit: ## Run unit tests
 	nosetests --nocapture tests/
 
+format: ## Format code automatically
+	black ./tutor
+
 ###### Deployment
 
 bundle: ## Bundle the tutor package in a single "dist/tutor" executable
@@ -37,7 +48,7 @@ ci-info: ## Print info about environment
 	python3 --version
 	pip3 --version
 
-ci-test: ## Run unit tests but without nosetests, which is not available on Mac OS in travis-ci
+ci-test: test-format test-lint ## Run unit tests but without nosetests, which is not available on Mac OS in travis-ci
 	python3 -m unittest discover tests
 
 ci-bundle: ## Create bundle and run basic tests

docs/tutor.rst

@@ -22,7 +22,22 @@ Run tests
 
     make test
 
-Yes, there are very few tests for now, but this is probably going to change.
+Yes, there are very few unit tests for now, but this is probably going to change.
+
+Code formatting
+---------------
+
+Tutor code formatting is enforced by `black <https://black.readthedocs.io/en/stable/>`_. To check whether your code changes conform to formatting standards, run::
+
+    make test-format
+
+And to automatically fix formatting errors, run::
+
+    make format
+
+Static error detection is performed by `pylint <https://pylint.readthedocs.io/en/latest/>`_. To detect errors, run::
+
+    make test-lint
 
 Bundle ``tutor`` executable
 ---------------------------

requirements/dev.in

@@ -1,4 +1,6 @@
 -r base.txt
+black
 nose
 pip-tools
+pylint
 pyinstaller

requirements/dev.txt

@@ -6,6 +6,9 @@
 #
 altgraph==0.16.1          # via macholib, pyinstaller
 appdirs==1.4.3
+astroid==2.2.5            # via pylint
+attrs==19.1.0             # via black
+black==19.3b0
 cachetools==3.1.0
 certifi==2019.3.9
 chardet==3.0.4
@@ -14,10 +17,13 @@ click==7.0
 future==0.17.1            # via pefile
 google-auth==1.6.3
 idna==2.8
+isort==4.3.18             # via pylint
 jinja2==2.10.1
 kubernetes==9.0.0
+lazy-object-proxy==1.3.1  # via astroid
 macholib==1.11            # via pyinstaller
 markupsafe==1.1.1
+mccabe==0.6.1             # via pylint
 nose==1.3.7
 oauthlib==3.0.1
 pefile==2018.8.8          # via pyinstaller
@@ -26,12 +32,16 @@ prompt-toolkit==2.0.9
 pyasn1-modules==0.2.4
 pyasn1==0.4.5
 pyinstaller==3.4
+pylint==2.3.1
 python-dateutil==2.8.0
 pyyaml==5.1
 requests-oauthlib==1.2.0
 requests==2.21.0
 rsa==4.0
 six==1.12.0
+toml==0.10.0              # via black
+typed-ast==1.3.5          # via astroid
 urllib3==1.24.2
 wcwidth==0.1.7
 websocket-client==0.56.0
+wrapt==1.11.1             # via astroid