Adds a version file

Author: babbush

cirq/__init__.py

@@ -141,6 +141,8 @@
     Timestamp,
 )
 
-# Import examples last, because they reference this top-level package.
-
+# Import examples second-to-last, because they reference this top-level package.
 from cirq import examples
+
+# Import version last since it is a relative import.
+from ._version import __version__

cirq/_version.py

@@ -0,0 +1,16 @@
+# Copyright 2018 Google LLC
+#
+# 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
+#
+#     https://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.
+
+"""Define version number here and read it from setup.py automatically"""
+__version__ = "0.1"

setup.py

@@ -14,13 +14,16 @@
 
 from setuptools import find_packages, setup
 
+# This reads the __version__ variable from cirq/_version.py
+exec(open('cirq/_version.py').read())
+
 # Read in requirements.txt
 requirements = open('requirements.txt').readlines()
 requirements = [r.strip() for r in requirements]
 
 setup(
     name='cirq',
-    version='0.1',
+    version=__version__,
     url='http://github.com/quantumlib/cirq',
     author='The Cirq Developers',
     install_requires=requirements,