An example implementation of an ETL registry

etl_regstry.py

class ETLRegistry(object):
    """ 
    The ETL registry stores the relationships between Extract, Transform
    and Load classes.
    
    An entry tracks both a string representation (for passing through message queue) and
    a reference for the class (for invocation inside the task)
    """

    _regsitry = []
    
    def register(self, extractor, transformer, loader):
        self._registry.append({
            'extractor': {
                'name': extractor.__name__,
                'class': extractor
            },
            'transformer': {
                'name': transformer.__name__,
                'class': transformer
            },
            'loader': {
                'name': loader.__name__,
                'class': loader
            }
        })
        
    def get_entry(self, **kwargs):
        """ Return a registry entry for the given ETL class type """
        if kwargs.get('extractor', False)
            for entry in self._registry:
                if entry['extractor']['name'] == kwargs['extractor']
                    return entry
                
        if kwargs.get('transformer', False)
            for entry in self._registry:
                if entry['transformer']['name'] == kwargs['transformer']
                    return entry
                
        if kwargs.get('loader', False)
            for entry in self._registry:
                if entry['loader']['name'] == kwargs['loader']
                    return entry

                    
etl_registry = ETLRegistry()
etl_registry.register(EmployeeExtractor, EmployeeTransformer, EmployeeLoader)
etl_registry.register(SaleExtractor, SaleTransformer, SaleLoader)