def support_count(itemset, transactions):
    """
    Count support count for itemset

    :param itemset: items to measure support count for
    :param transactions: list of sets (all transactions)

    >>> simple_transactions = ['ABC', 'BC', 'BD', 'D']
    >>> [support_count(item, simple_transactions) for item in 'ABCDE']
    [1, 3, 2, 2, 0]
    >>> some_transactions = [set(['beer', 'bread', 'milk']), set(['beer']), set(['milk'])]
    >>> support_count(set(['beer']), some_transactions)
    2
    """
    return len([row for row in transactions if set(itemset) <= set(row)])