def describe_event_categories(SourceType=None):
    """
    Displays a list of event categories for all event source types, or for a specified source type. For a list of the event categories and source types, go to Amazon Redshift Event Notifications .
    See also: AWS API Documentation
    
    
    :example: response = client.describe_event_categories(
        SourceType='string'
    )
    
    
    :type SourceType: string
    :param SourceType: The source type, such as cluster or parameter group, to which the described event categories apply.
            Valid values: cluster, cluster-snapshot, cluster-parameter-group, and cluster-security-group.
            

    :rtype: dict
    :return: {
        'EventCategoriesMapList': [
            {
                'SourceType': 'string',
                'Events': [
                    {
                        'EventId': 'string',
                        'EventCategories': [
                            'string',
                        ],
                        'EventDescription': 'string',
                        'Severity': 'string'
                    },
                ]
            },
        ]
    }
    
    
    """
    pass
