Cyber: Add Python version check to wrappers.

cyber/python/cyber_py/__init__.py

+#!/usr/bin/env python2
+
+# ****************************************************************************
+# Copyright 2019 The Apollo Authors. All Rights Reserved.
+#
+# Licensed 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.
+# ****************************************************************************
+
+import sys
+
+
+if sys.version_info[0] >= 3:
+    sys.stderr.write('''
+        You are running Python3 while importing Python2 Cyber wrapper!
+        Please change to "import cyber_py3.xyz" accordingly.''')
+    sys.exit(1)

cyber/python/cyber_py3/__init__.py

+#!/usr/bin/env python3
+
+# ****************************************************************************
+# Copyright 2019 The Apollo Authors. All Rights Reserved.
+#
+# Licensed 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.
+# ****************************************************************************
+
+import sys
+
+
+if sys.version_info[0] < 3:
+    sys.stderr.write('''
+        You are running Python2 while importing Python3 Cyber wrapper!
+        Please change to "import cyber_py.xyz" accordingly.''')
+    sys.exit(1)