Data toy: Apriori algorithm in Python

apriori_toy.py

from collections import Counter
from itertools import combinations

def distinct_items(transactions, support=None):
    """Returns counted set of distinct items in transactions"""
    counter = Counter()
    for trans in transactions:
        counter.update(trans)

    if support is not None:
        return set(item for item in counter if counter[item] >= support)
    else:
        return set(counter)

def frequent_single_itemsets(transactions, support):
    """Return one-item itemsets with at least `support` support."""
    distinct = distinct_items(transactions, support)
    return set(frozenset([i]) for i in distinct)

def generate_candidates(L, k):
    """Generate candidate set from `L` with size `k`"""
    candidates = set()
    for a in L:
        for b in L:
            union = a | b
            if len(union) == k and a != b:
                candidates.add(union)
    return candidates

def itemsets_support(transactions, itemsets):
    """Get support for `itemsets`"""

    support_set = Counter()

    for trans in transactions:
        subsets = [itemset for itemset in itemsets if itemset < trans]
        support_set.update(subsets)

    return support_set

def min_support_set(counter, support):
    """Return sets with minimal `support`"""
    items = [item for item in counter if counter[item] >= support]
    return set(items)

def apriori(transactions, support):
    candidates = frequent_single_itemsets(transactions, support)
    result = list()

    k = 2
    while candidates:
        # Get candidate set
        candidates = generate_candidates(candidates, k)
        supported = itemsets_support(transactions, candidates)
        candidates = min_support_set(supported, support)
        result += candidates
        k += 1

    return result

I wanted to know what is the data type of variable "transactions" in the above code. Also please tell me how to call the function Apriori.

Thank you for the coding. It works perfectly after modifying from:
subsets = [itemset for itemset in itemsets if itemset < trans]
to:
subsets = [itemset for itemset in itemsets if itemset <= trans]