[Feature] Flake8' tool to perform additional formatting and semantic checking of code.

.flake8

@@ -0,0 +1,43 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+[flake8]
+select = B,C,E,F,P,T4,W,B9
+max-line-length = 120
+ignore = E203,E305
+optional-ascii-coding = True
+exclude =
+    ./.git,
+    ./.github,
+    ./3rdparty,
+    ./benchmark,
+    ./cd,
+    ./ci,
+    ./cmake,
+    ./config,
+    ./contrib,
+    ./cpp-package,
+    ./docker,
+    ./docs,
+    ./example,
+    ./include,
+    ./licences,
+    ./plugin,
+    ./src,
+    ./tools,
+    ./build,
+    *.pyi

ci/docker/runtime_functions.sh

@@ -704,6 +704,7 @@ sanity_check() {
     sanity_clang
     sanity_license
     sanity_python
+    sanity_python_flake8
     sanity_cpp
 }
 
@@ -712,6 +713,22 @@ sanity_license() {
     tools/license_header.py check
 }
 
+sanity_python_flake8() {
+    set -ex
+
+    # Install dependencies
+    pip3 install -r requirements-flake8.txt --user
+
+    # Run flake8
+    python3 -m flake8 | tee flake8-output.txt
+
+    if [ -s flake8-output.txt ]; then
+        echo 'Please fix the above Flake8 warnings.'
+        exit 1
+    fi
+    exit 0
+}
+
 sanity_cpp() {
     set -ex
     3rdparty/dmlc-core/scripts/lint.py mxnet cpp include src plugin cpp-package tests --exclude_path src/operator/contrib/ctc_include include/onednn

requirements-flake8.txt

@@ -0,0 +1,5 @@
+flake8==3.8.2
+flake8-pyi==20.5.0
+flake8-bugbear==20.1.4
+flake8-comprehensions==3.3.0
+flake8-executable==2.0.4

tools/git-pre-commit

@@ -20,3 +20,6 @@ set -e
 
 echo "Running pre-commit clang-format"
 tools/lint/git-clang-format HEAD~ --force
+
+echo "Running pre-commit flake8 checker"
+python tools/lint/flake8_hook.py

tools/lint/flake8_hook.py

@@ -0,0 +1,44 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+#!/usr/bin/env python3
+
+import sys
+
+from flake8.main import git
+
+if __name__ == '__main__':
+    sys.exit(
+        git.hook(
+            # (optional):
+            # any value > 0 enables complexity checking with mccabe
+            complexity=0,
+
+            # (optional):
+            # if True, this returns the total number of error which will cause
+            # the hook to fail
+            strict=True,
+
+            # (optional):
+            # a comma-separated list of errors and warnings to ignore
+            # ignore=
+
+            # (optional):
+            # allows for the instances where you don't add the the files to the
+            # index before running a commit, e.g git commit -a
+            lazy=git.config_for('lazy'),
+        )
+    )