Introduce some static type analysis to the codebase

jstasiak · jstasiak · commit 1f33c4f8a805 · 2018-09-12T15:30:21.000+02:00
The main purpose of this change is to make the code easier to read and
explore. Preventing some classes of bugs is a bonus.

On top of just adding type hints and enabling mypy to verify them the
following changes were needed:
* casts in places where we know what we're doing but mypy can't know it
* RecordUpdateListener interfaces extracted out of ServiceBrowser and
  ServiceInfo classes so that we have a common name we can use in places
  where we only need an instance of one of those classes to call to call
  update_record() on it. This way we can keep mypy happy
* assert isinstance(...) blocks to provide hints for mypy as to what
  concrete types we're dealing with
* some local type mixing removed (previously we'd first assign a value
  of one type to a variable and then overwrite with another type)
* explicit "return None" in case of function that returns optionally -
  mypy enforces explicit return in this case
diff --git a/.gitignore b/.gitignore
@@ -9,4 +9,4 @@ Thumbs.db
 .idea
 .vslick
 .cache
-
+.mypy_cache/
diff --git a/.travis.yml b/.travis.yml
@@ -8,9 +8,12 @@ matrix:
     fast_finish: true
 install:
     - pip install -r requirements-dev.txt
+    # mypy can't be installed on pypy
+    - if [[ "${TRAVIS_PYTHON_VERSION}" != "pypy3.5-5.8.0" ]] ; then pip install mypy ; fi
 script:
     - make test_coverage
     - flake8 --version
     - make flake8
+    - if [[ "${TRAVIS_PYTHON_VERSION}" != "pypy3.5-5.8.0" ]] ; then make mypy ; fi
 after_success:
     - coveralls
diff --git a/Makefile b/Makefile
@@ -13,6 +13,9 @@ env:
 flake8:
 	flake8 --max-line-length=$(MAX_LINE_LENGTH) examples *.py
 
+mypy:
+	mypy examples/*.py zeroconf.py
+
 test:
 	nosetests -v
 
diff --git a/examples/browser.py b/examples/browser.py
@@ -6,17 +6,20 @@
 import socket
 import sys
 from time import sleep
+from typing import cast
 
 from zeroconf import ServiceBrowser, ServiceStateChange, Zeroconf
 
 
-def on_service_state_change(zeroconf, service_type, name, state_change):
+def on_service_state_change(
+    zeroconf: Zeroconf, service_type: str, name: str, state_change: ServiceStateChange,
+) -> None:
     print("Service %s of type %s state changed: %s" % (name, service_type, state_change))
 
     if state_change is ServiceStateChange.Added:
         info = zeroconf.get_service_info(service_type, name)
         if info:
-            print("  Address: %s:%d" % (socket.inet_ntoa(info.address), info.port))
+            print("  Address: %s:%d" % (socket.inet_ntoa(cast(bytes, info.address)), cast(int, info.port)))
             print("  Weight: %d, priority: %d" % (info.weight, info.priority))
             print("  Server: %s" % (info.server,))
             if info.properties:
diff --git a/examples/self_test.py b/examples/self_test.py
@@ -29,9 +29,9 @@
         r.get_service_info("_http._tcp.local.", "ZOE._http._tcp.local.")))
     print("   Query done.")
     print("3. Testing query of own service...")
-    info = r.get_service_info("_http._tcp.local.", "My Service Name._http._tcp.local.")
-    assert info
-    print("   Getting self: %s" % (info,))
+    queried_info = r.get_service_info("_http._tcp.local.", "My Service Name._http._tcp.local.")
+    assert queried_info
+    print("   Getting self: %s" % (queried_info,))
     print("   Query done.")
     print("4. Testing unregister of service information...")
     r.unregister_service(info)
diff --git a/mypy.ini b/mypy.ini
@@ -0,0 +1,7 @@
+[mypy]
+ignore_missing_imports = true
+follow_imports = error
+warn_no_return = true
+warn_redundant_casts = true
+# TODO: disallow untyped defs once we have full type hint coverage
+disallow_untyped_defs = false
diff --git a/requirements-dev.txt b/requirements-dev.txt
@@ -4,7 +4,6 @@ coverage
 flake8
 flake8-blind-except
 flake8-import-order
-mypy
 # See setup.py comment for why this version is restricted
 netifaces!=0.10.5
 nose
diff --git a/zeroconf.py b/zeroconf.py

-Original file line number
+Diff line change
 .idea
 .vslick
 .cache
+-
 +.mypy_cache/