Enable static type checking with pytype (#298)

* Ignore pytype import errors in google/auth.

These errors are raised because the packages are not required, i.e. not
listed in setup.py. We can't guarantee they'll be installed or that
their pyi files exist in github.com/python/typeshed, so silence
potential errors instead.

This does impact the accuracy of type checking.

* Ignore pytype import errors in transport/.

These imports are not listed in setup.py, because they are optional --
it is assumed the user has them installed if needed. Disabling
import-error for these imports prevents useless errors from pytype.

* Ignore various type errors raised by pytype.

- `__init__.py`: pytype is not aware of `__path__`.
- jwt.py: the pyi file for urllib.unparse is not aware of None. Empty
strings are clearer.

* Add pytype disable comments for scripts/

oauth2client isn't listed as a requirement, so users may not have it
installed.

* Fix lint errors from pytype directives.

* Enable pytype -V3.6.

A few notes:
- Previous commits fixed type errors detected by pytype.
- setup.cfg disables pytype's `pyi-error`. This is necessary due to
incomplete type stubs in https://github.com/python/typeshed.
- This only enables pytype's Python3.6 checks. Python2.7 is supported by
pytype but incomplete type stubs cause spurious type errors.

* Remove pytype directives.

Updates to pytype made these directives unnecessary.

* Move pytype install command.

* Add pytype to tox.

* Remove pytype directives for tox-installed imports.

These imports are handled by setup.py and tox.ini, so they'll be
available when pytype is run under tox.

* Fix lint error.

1 files changed, 15 insertions, 0 deletions

diff --git a/setup.cfg b/setup.cfg
index 2a9acf1..0f15a38 100644
--- a/setup.cfg
+++ b/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