'Modifies an existing RDS event notification subscription. Note
that you cannot modify the source identifiers using this call;
to change source identifiers for a subscription, use the
AddSourceIdentifierToSubscription and
RemoveSourceIdentifierFromSubscription calls.
You can see a list of the event categories for a given
SourceType in the `Events`_ topic in the Amazon RDS User Guide
or by using the **DescribeEventCategories** action.
:type subscription_name: string
:param subscription_name: The name of the RDS event notification
subscription.
:type sns_topic_arn: string
:param sns_topic_arn: The Amazon Resource Name (ARN) of the SNS topic
created for event notification. The ARN is created by Amazon SNS
when you create a topic and subscribe to it.
:type source_type: string
:param source_type: The type of source that will be generating the
events. For example, if you want to be notified of events generated
by a DB instance, you would set this parameter to db-instance. if
this value is not specified, all events are returned.
Valid values: db-instance | db-parameter-group | db-security-group |
db-snapshot
:type event_categories: list
:param event_categories: A list of event categories for a SourceType
that you want to subscribe to. You can see a list of the categories
for a given SourceType in the `Events`_ topic in the Amazon RDS
User Guide or by using the **DescribeEventCategories** action.
:type enabled: boolean
:param enabled: A Boolean value; set to **true** to activate the
subscription.'

def modify_event_subscription(self, subscription_name, sns_topic_arn=None, source_type=None, event_categories=None, enabled=None):

    params = {'SubscriptionName': subscription_name}
    if (sns_topic_arn is not None):
        params['SnsTopicArn'] = sns_topic_arn
    if (source_type is not None):
        params['SourceType'] = source_type
    if (event_categories is not None):
        self.build_list_params(params, event_categories, 'EventCategories.member')
    if (enabled is not None):
        params['Enabled'] = str(enabled).lower()
    return self._make_request(action='ModifyEventSubscription', verb='POST', path='/', params=params)
