human
Complete this python program:
def get_num_instances(module=None, version=None):
assistant
#Here is the Python code you requested.

    """Return the number of instances that are set for the given module version.
    This is only valid for fixed modules, an error will be raised for
    automatically-scaled modules.  Support for automatically-scaled modules may be
    supported in the future.
    Args:
    module: String containing the name of the module to fetch this info for, if
    None the module of the current instance will be used.
    version: String containing the name of the version to fetch this info for,
    if None the version of the current instance will be used.  If that version
    does not exist in the other module, then an InvalidVersionError is raised.
    Returns:
    The number of instances that are set for the given module version.
    Raises:
    InvalidVersionError on invalid input.
    """
    def _ResultHook(rpc):
        mapped_errors = [modules_service_pb.ModulesServiceError.INVALID_VERSION]
        _CheckAsyncResult(rpc, mapped_errors, {})
        return rpc.response.instances()
    request = modules_service_pb.GetNumInstancesRequest()
    if module:
        request.set_module(module)
    if version:
        request.set_version(version)
    response = modules_service_pb.GetNumInstancesResponse()
    return _MakeAsyncCall('GetNumInstances', request, response, _ResultHook).get_result()