def avg_freq_from_files(fnames):
    assert(len(fnames))
    freqs = [count_freq_for_str(open(i).read()) for i in fnames]
    cmn_keys = set(freqs[0].keys())
    for i in freqs[1:]:
        cmn_keys = cmn_keys.intersection(set(i.keys()))
    def avg_fr(n):
        return avg([i[n] for i in freqs])
    freq = dict((k, avg_fr(k)) for k in cmn_keys)
    return freq

const std::map<int, double> avg_freq_from_files(std::vector<string> &fnames)
{
    std::map<int, double> freq, f1;
    std::vector< std::map<int,double> > freqs;
    std::set<int> cmn_keys, cmn_keys1;
    std::vector<string> words;
    size_t i;
    string str;
    char s;
    string word; 
    
    if (fnames.size() == 0)
        exit(1);
        
    for (i=0; i<fnames.size(); i++)
    {
        ifstream input_file(fnames[i].c_str(), ifstream::in ); 
        while (! input_file.eof())
        { 
            s = input_file.get();       
            if ((s>='a' && s<='z')||(s>='A' && s<='Z'))
            {    
                word += s; 
            }        
            else 
            {   
                if (word.size() != 0)
                {
                    f1 = count_freq_for_str<int>(word); 
                    freqs.push_back(f1);
                }
                word.clear();
            } 
        }
        input_file.close(); 
    } 
    cmn_keys = get_keys(freqs[0]);
         //?????
    for(i=1; i<freqs.size(); i++)
    {
        std::set<int> cmn_keys2;
        cmn_keys1 = get_keys(freqs[i]);
        set_intersection(cmn_keys.begin(), cmn_keys.end(), cmn_keys1.begin(), cmn_keys1.end(),
            inserter(cmn_keys2, cmn_keys2.begin()));
        cmn_keys = cmn_keys2;
    }
    
    
    for (i = 0; i<cmn_keys.size(); i++)
    {
        freq.insert(std::pair<int, double> (i, avg_fr(i, freqs)));
    }
    
    return freq;
}

for i in freqs[1:]:
        cmn_keys = cmn_keys.intersection(set(i.keys()))