Add mypy linting to the CI pipeline

Signed-off-by: Chris Marchbanks <[email protected]>

.circleci/config.yml

@@ -19,6 +19,12 @@ jobs:
       - checkout
       - run: pip install tox
       - run: tox -e isort
+  mypy_lint:
+    executor: python
+    steps:
+      - checkout
+      - run: pip install tox
+      - run: tox -e mypy
   test:
     parameters:
       python:
@@ -64,6 +70,7 @@ workflows:
     jobs:
       - flake8_lint
       - isort_lint
+      - mypy_lint
       - test:
           matrix:
             parameters:

mypy.ini

@@ -0,0 +1,5 @@
+[mypy]
+exclude = prometheus_client/decorator.py|prometheus_client/twisted|tests/test_twisted.py
+
+[mypy-prometheus_client.decorator]
+follow_imports = skip

tests/test_core.py

@@ -1,5 +1,6 @@
 from concurrent.futures import ThreadPoolExecutor
 import time
+import unittest
 
 import pytest
 
@@ -11,11 +12,6 @@
 )
 from prometheus_client.decorator import getargspec
 
-try:
-    import unittest2 as unittest
-except ImportError:
-    import unittest
-
 
 def assert_not_observable(fn, *args, **kwargs):
     """

tests/test_exposition.py

@@ -1,3 +1,4 @@
+from http.server import BaseHTTPRequestHandler, HTTPServer
 import threading
 import time
 import unittest
@@ -15,12 +16,6 @@
     passthrough_redirect_handler,
 )
 
-try:
-    from BaseHTTPServer import BaseHTTPRequestHandler, HTTPServer
-except ImportError:
-    # Python 3
-    from http.server import BaseHTTPRequestHandler, HTTPServer
-
 
 class TestGenerateText(unittest.TestCase):
     def setUp(self):

tests/test_graphite_bridge.py

@@ -1,14 +1,10 @@
+import socketserver as SocketServer
 import threading
 import unittest
 
 from prometheus_client import CollectorRegistry, Gauge
 from prometheus_client.bridge.graphite import GraphiteBridge
 
-try:
-    import SocketServer
-except ImportError:
-    import socketserver as SocketServer
-
 
 def fake_timer():
     return 1434898897.5

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = coverage-clean,py3.6,py3.7,py3.8,py3.9,py3.10,pypy3.7,py3.9-nooptionals,coverage-report,flake8,isort
+envlist = coverage-clean,py3.6,py3.7,py3.8,py3.9,py3.10,pypy3.7,py3.9-nooptionals,coverage-report,flake8,isort,mypy
 
 
 [base]
@@ -48,6 +48,15 @@ skip_install = true
 commands =
     isort --check prometheus_client/ tests/ setup.py
 
+[testenv:mypy]
+deps =
+    pytest
+    asgiref
+    mypy==0.910
+skip_install = true
+commands =
+    mypy --install-types --non-interactive prometheus_client/ tests/
+
 [flake8]
 ignore =
     D,