Enable static type checking with pytype

.gitignore

@@ -35,3 +35,4 @@ tests/data/user-key.json
 # Generated files
 pylintrc
 pylintrc.test
+pytype_output/

.travis.yml

@@ -22,6 +22,8 @@ matrix:
  env: TOXENV=py36-system SYSTEM_TEST=1 SKIP_APP_ENGINE_SYSTEM_TEST=1
  - python: 2.7
  env: TOXENV=py27-system SYSTEM_TEST=1 SKIP_APP_ENGINE_SYSTEM_TEST=1
+ - python: 3.6
+ env: TOXENV=pytype
 cache:
  directories:
  - ${HOME}/.cache

google/auth/_oauth2client.py

@@ -25,6 +25,7 @@
 
 from google.auth import _helpers
 import google.auth.app_engine
+import google.auth.compute_engine
 import google.oauth2.credentials
 import google.oauth2.service_account
 
@@ -37,7 +38,7 @@
  ImportError('oauth2client is not installed.'), caught_exc)
 
 try:
- import oauth2client.contrib.appengine
+ import oauth2client.contrib.appengine # pytype: disable=import-error
  _HAS_APPENGINE = True
 except ImportError:
  _HAS_APPENGINE = False

google/auth/app_engine.py

@@ -28,10 +28,12 @@
 from google.auth import credentials
 from google.auth import crypt
 
+# pytype: disable=import-error
 try:
  from google.appengine.api import app_identity
 except ImportError:
  app_identity = None
+# pytype: enable=import-error
 
 
 class Signer(crypt.Signer):

google/auth/jwt.py

@@ -738,7 +738,7 @@ def before_request(self, request, method, url, headers):
  parts = urllib.parse.urlsplit(url)
  # Strip query string and fragment
  audience = urllib.parse.urlunsplit(
- (parts.scheme, parts.netloc, parts.path, None, None))
+ (parts.scheme, parts.netloc, parts.path, "", ""))
  token = self._get_jwt_for_audience(audience)
  self.apply(headers, token=token)
 

setup.cfg

@@ -1,2 +1,17 @@
 [bdist_wheel]
 universal = 1
+
+[pytype]
+# Where to start analysis.
+inputs = .
+# Some files aren't worth analyzing, namely tests. Hidden directories (e.g.
+# .tox) are automatically filtered out.
+exclude = tests system_tests
+# All pytype output goes here.
+output = pytype_output
+# Python version (major.minor) of the target code.
+python_version = 3.6
+# Paths to source code directories, separated by ':'.
+pythonpath = .
+# Errors to disable.
+disable = pyi-error

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = lint,py27,py34,py35,py36,pypy,cover
+envlist = lint,py27,py34,py35,py36,pypy,cover,pytype
 
 [testenv]
 deps =
@@ -82,3 +82,11 @@ deps =
  flake8
  flake8-import-order
  docutils
+
+[testenv:pytype]
+basepython = python3.6
+commands =
+ pytype
+deps =
+ {[testenv]deps}
+ pytype