def __init__(self, transactions):
self.__num_transaction = <NUM_LIT:0><EOL>self.__items = []<EOL>self.__transaction_index_map = {}<EOL>for transaction in transactions:<EOL><INDENT>self.add_transaction(transaction)<EOL><DEDENT>
Initialize.

Arguments:
    transactions -- A transaction iterable object
                    (eg. [['A', 'B'], ['B', 'C']]).