subsets.py

def subsets(s):
    '''
    This function returns all the possible subsets of a set of channels.
    input :
            - s: a set of channels.
    '''
    if len(s)==1:
        return s
    else:
        sub_channels=[]
        for i in range(1,len(s)+1):
            sub_channels.extend(map(list,itertools.combinations(s, i)))
    return map(",".join,map(sorted,sub_channels))