C++とpythonの比較(3)

#include <iostream>
#include <vector>
#include <unordered_map>
#include <regex>

using namespace std;

struct opt_info
{
    bool f_term;
    const int const_value;
    const int default_value;
    const char *help;
};

unordered_map<string, struct opt_info> option_lt = {
    {"--help", {true, 0, 0, "help message"}},       // help message
    {"--special", {false, 3, 1, "special option"}}, // const value = 3, default = 1
    {"--hogen", {false, 4, 1, "hogen option"}},     // const value = 4, default = 1
};

int main(int argc, char **argv)
{
    vector<string> lt;
    if (argc > 1)
    {
        int n = argc - 1;
        for (int i = 0; i < n; i++)
        {
            lt.push_back(argv[i + 1]);
        }
    }
    else
    {
        return 0;
    }

    unordered_map<string, int> opt_val_lt;
    unordered_map<string, bool> check_lt;

    decltype(option_lt)::iterator it = option_lt.begin();
    for (; it != option_lt.end(); ++it)
    {
        check_lt.insert(make_pair(it->first, false));
    }

    bool term = false;
    decltype(lt)::iterator k = lt.begin();
    for (; k != lt.end(); ++k)
    {
        decltype(option_lt)::iterator it = option_lt.find(*k);
        if (it != option_lt.end())
        {
            if (it->second.f_term)
            {
                term = true;
            }
            check_lt[it->first] = true;
        }
    }

    it = option_lt.begin();
    for (; it != option_lt.end(); ++it)
    {
        string s = it->first;
        regex reg{R"(--)"};
        string ret = regex_replace(s, reg, "");
        if (check_lt[it->first])
        {
            opt_val_lt.insert(make_pair(ret, it->second.const_value));
        }
        else
        {
            opt_val_lt.insert(make_pair(ret, it->second.default_value));
        }
    }

    if (0 == opt_val_lt.size())
    {
        cerr << "unknown option" << endl;
        return -1;
    }

    if (term)
    {
        it = option_lt.begin();
        cerr << "Help:" << endl;
        for (; it != option_lt.end(); ++it)
        {
            cerr << "    " << it->first << " : " << it->second.help << endl;
        }
        return 0;
    }

    decltype(opt_val_lt)::iterator e = opt_val_lt.begin();
    for (; e != opt_val_lt.end(); ++e)
    {
        cout << e->first << " : " << e->second << endl;
    }

    try
    {
        cout << opt_val_lt.at("special") << endl; // use value of special
        cout << opt_val_lt.at("hogen") << endl;   // use value of hogen
    }
    catch (std::out_of_range &)
    {
        cerr << "exception std::out_of_range" << endl;
    }

    return 0;
}

import argparse

parser = argparse.ArgumentParser()
parser.add_argument(
    "--special", type=int, nargs="?", const=3, default=1, help="special option"
)
parser.add_argument(
    "--hogen", type=int, nargs="?", const=4, default=1, help="hogen option"
)

opt = parser.parse_args()

print(opt)
print(f"special = {opt.special}")  # use value of special
print(f"hogen   = {opt.hogen}")  # use value of hogen