export a __version__ variable for python module (#5309)

* export a __version__ variable for python module

* assign version to be used below

* better support python2

* Add copyright header

python/flatbuffers/__init__.py

@@ -15,4 +15,5 @@
 from .builder import Builder
 from .table import Table
 from .compat import range_func as compat_range
+from ._version import __version__
 from . import util

python/flatbuffers/_version.py

@@ -0,0 +1,17 @@
+# Copyright 2019 Google Inc. 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.
+
+# Placeholder, to be updated during the release process
+# by the setup.py
+__version__ = u"latest"

python/setup.py

@@ -12,18 +12,28 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import fileinput
 import os
+import re
+import sys
 from datetime import datetime
 from setuptools import setup
 
 
+def _update_version_attr(new_version):
+    for line in fileinput.input('flatbuffers/_version.py', inplace=True):
+        if line.startswith('__version__'):
+            line = re.sub(r'".*"', '"{}"'.format(new_version), line)
+        sys.stdout.write(line)
+
+
 def version():
     version = os.getenv('VERSION', None)
     if version:
         # Most git tags are prefixed with 'v' (example: v1.2.3) this is
         # never desirable for artifact repositories, so we strip the
         # leading 'v' if it's present.
-        return version[1:] if version.startswith('v') else version
+        version = version[1:] if version.startswith('v') else version
     else:
         # Default version is an ISO8601 compiliant datetime. PyPI doesn't allow
         # the colon ':' character in its versions, and time is required to allow
@@ -39,8 +49,11 @@ def version():
         print("VERSION environment variable not set, using datetime instead: {}"
               .format(version))
 
+    _update_version_attr(version)
+
     return version
 
+
 setup(
     name='flatbuffers',
     version=version(),