Added Pylint to sanity tests

Pylint is only enabled for "grpcio/grpc" package,
and various specific checks that currently fail are disabled,
each with a respective TODO item in the .pylintrc file.

.pylintrc

+[MESSAGES CONTROL]
+
+#TODO: Enable missing-docstring
+#TODO: Enable too-few-public-methods
+#TODO: Enable too-many-arguments
+#TODO: Enable no-init
+#TODO: Enable duplicate-code
+#TODO: Enable invalid-name
+#TODO: Enable suppressed-message
+#TODO: Enable locally-disabled
+#TODO: Enable protected-access
+#TODO: Enable no-name-in-module
+#TODO: Enable unused-argument
+#TODO: Enable fixme
+#TODO: Enable wrong-import-order
+#TODO: Enable no-value-for-parameter
+#TODO: Enable cyclic-import
+#TODO: Enable unused-variable
+#TODO: Enable redefined-outer-name
+#TODO: Enable unused-import
+#TODO: Enable too-many-instance-attributes
+#TODO: Enable broad-except
+#TODO: Enable too-many-locals
+#TODO: Enable too-many-lines
+#TODO: Enable redefined-variable-type
+#TODO: Enable next-method-called
+#TODO: Enable import-error
+#TODO: Enable useless-else-on-loop
+#TODO: Enable too-many-return-statements
+#TODO: Enable too-many-nested-blocks
+#TODO: Enable super-init-not-called
+#TODO: Enable simplifiable-if-statement
+#TODO: Enable no-self-use
+#TODO: Enable no-member
+#TODO: Enable logging-format-interpolation
+#TODO: Enable dangerous-default-value
+
+disable=missing-docstring,too-few-public-methods,too-many-arguments,no-init,duplicate-code,invalid-name,suppressed-message,locally-disabled,protected-access,no-name-in-module,unused-argument,fixme,wrong-import-order,no-value-for-parameter,cyclic-import,unused-variable,redefined-outer-name,unused-import,too-many-instance-attributes,broad-except,too-many-locals,too-many-lines,redefined-variable-type,next-method-called,import-error,useless-else-on-loop,too-many-return-statements,too-many-nested-blocks,super-init-not-called,simplifiable-if-statement,no-self-use,no-member,logging-format-interpolation,dangerous-default-value

tools/distrib/pylint_code.sh

+#!/bin/bash
+# Copyright 2017, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+set -ex
+
+# change to root directory
+cd $(dirname $0)/../..
+
+DIRS=src/python/grpcio/grpc
+
+VIRTUALENV=python_pylint_venv
+
+virtualenv $VIRTUALENV
+PYTHON=`realpath $VIRTUALENV/bin/python`
+$PYTHON -m pip install pylint==1.6.5
+
+for dir in $DIRS; do
+  $PYTHON -m pylint --rcfile=.pylintrc -rn $dir || exit $?
+done
+
+exit 0

tools/run_tests/sanity/sanity_tests.yaml

@@ -12,6 +12,7 @@
 - script: tools/distrib/check_trailing_newlines.sh
 - script: tools/distrib/check_nanopb_output.sh
 - script: tools/distrib/check_include_guards.py
+- script: tools/distrib/pylint_code.sh
 - script: tools/distrib/yapf_code.sh
 - script: tools/distrib/python/check_grpcio_tools.py