def create_substitutes(logs_location_base, storage_location_base,
    dynamodb_table_name):
    """Return an object which can be used to replace strings in the policy
    files

    The two *_base strings are expected to be bucket/path representations
    Current strings supported are:
    - ${DATALAKE_BUCKET}
    - ${DYNAMODB_TABLE_NAME}
    - ${LOGS_LOCATION_BASE}
    - ${STORAGE_LOCATION_BASE}

"""
    s = {'LOGS_LOCATION_BASE': logs_location_base, 'STORAGE_LOCATION_BASE':
        storage_location_base, 'DYNAMODB_TABLE_NAME': dynamodb_table_name,
        'DATALAKE_BUCKET': storage_location_base.split('/')[0]}
    return s
