Only define version in one place

def find_version():
    """Only define version in one place"""
    version_file = read_file('__init__.py')
    version_match = re.search(r'^__version__ = ["\']([^"\']*)["\']',
                              version_file, re.M)
    if version_match:
        return version_match.group(1)
    raise RuntimeError('Unable to find version string.')