Good extraction of get_support() as a standalone helper — makes the
logic much easier to test in isolation. However, it's missing type
hints and a docstring. Suggestion:

def get_support(itemset: frozenset, transactions: list[set]) -> int:
"""Return the number of transactions containing the itemset."""
return sum(1 for t in transactions if itemset.issubset(t))

got it !

Using defaultdict(int) here is cleaner than the old counts = [0] *
len(itemset) approach — no more index tracking with enumerate().

One suggestion: the support counting loop (lines 93-96) could use
the new get_support() helper you defined earlier to avoid duplication
and keep the main apriori() function cleaner:

frequent = {
c: get_support(c, transactions)
for c in candidates
if get_support(c, transactions) >= min_support
}

Actual logic

The actual implementation is optimal:

for t in transactions:
    for c in candidates:
        if c.issubset(t):
            candidate_counts[c] += 1

It passes over each transactions once, count all candidates at once, and avoid repeated scans, which make it algorithmically better.

Your suggestion

frequent = {
    c: get_support(c, transactions)
    for c in candidates
    if get_support(c, transactions) >= min_support
}

It calls the get_suppor() twice per candidate, which literally double the cost:

• once in if
• once in the value

So it improves readability, but definitely not the performance.

Aligned with your suggestion

candidate_counts = {}

for c in candidates:
    support = get_support(c, transactions)
    if support >= min_support:
        candidate_counts[c] = support

Here we computes support only once avoiding duplications, but we keep the logic readable. This way, we assure readability and performance.