Get the version of `package` (by extracting it from the source code).

def get_version():
    """Get the version of `package` (by extracting it from the source code)."""
    module_path = get_absolute_path('pip_save', '__init__.py')
    with open(module_path) as handle:
        for line in handle:
            match = re.match(r'^__version__\s*=\s*["\']([^"\']+)["\']$', line)
            if match:
                return match.group(1)
    raise Exception("Failed to extract version from %s!" % module_path)