How to extract the value from a frozen set that was converted to a string with python?

Question

I am working on a python map/reduce in multiple parts.

My first map prints to the stdin so that the first reduce can pick it up.

The result of the map looks like this:

frozenset([4]) 14

The reduce reads in frozenset([4]) as the key, and 14 as the value.

How can I extract just the [4] from the key to pass to the output of the reduce? The map looks like this:

    import sys

    data = sys.stdin.read()
    dataset = []
    for line in data.splitlines():
        dataset.append(map(int, line.strip().split(" ")))

    c1 = []
    for transaction in dataset:
        for item in transaction:
            if not [item] in c1:
                c1.append([item])

    candidates = map(frozenset, c1)    

    sscnt = {}
    for tid in dataset:
        for can in candidates:
            if can.issubset(tid):
                sscnt.setdefault(can, 0)
                sscnt[can] += 1

    for key,val in sscnt.items():
        print key, val

The reduce looks like this:

    import sys

    min_support = 12
    sscnt = {}
    for input_line in sys.stdin:
        input_line = input_line.strip()
        key, value = input_line.split(" ")
        key = int(key)
        sscnt[key] = int(value)

    retlist = []
    for key in sscnt:
        support = sscnt[key]
        if value >= min_support:
            retlist.insert(0, key)

    print retlist

The output from the reduce looks like this:

    ['frozenset([1])', 'frozenset([4])', 'frozenset([2])']

The input data looks like this:

    1 2 3 5 8
    2 3 4 7
    1 2 4 5 7
    1 2 4 6 7
    1 2 3 4 5
    1 2 4 5 6
    1 2 4 6 9
    1 2 4 8
    3 5 6 8
    1 2 4 7
    1 2 4 5
    1 2 4 9
    3 5 6 9
    1 2 4 7
    3 5 6
    1 2 4 8
    1 5 6
    3 5 9
    1 2 4 6
    4 5 6 7

Answer 1

Does eval works for you?

Signature: eval(source, globals=None, locals=None, /)

Docstring: Evaluate the given source in the context of globals and locals.

list(eval('frozenset([1])'))

Returns:

[1]