Python vs C Plus Plus example

The main point here is to show how some of the more advanced C++ features map to Python code. The point is not what the code does (thus no comments), but how it does it. The example codes should be easily comparable, due to same variable and function names. The C++ code is about twice as long as the Python code, and runs about 7.5 times faster.

C++ code

include 
include 
include 
include 
include 
include 
include 
include 



using namespace std;

typedef multimap DicMap;
typedef vector Answers;

char toNumber(char letter) {
  static string letter2digit[] = { "E", "JNQ", "RWX", "DSY", "FT", "AM", "CIV", "BKU", "LOP", "GHZ" };
  for (int i = 0; i < 10; ++i)
    if (letter2digit[i].find(letter) != string::npos)
      return '0' + i;
  return '0';
}

void findMatch(const string& answer, const string& line, const DicMap& dic,
               bool allowNumber, Answers& answers) {
  if (line.empty()) {
    if (answer.length() != 0)
      answers.push_back(answer);
    return;
  }

  for (size_t i = 1; i <= line.length(); ++i) {
    pair range = dic.equal_range(line.substr(0, i));
    for (DicMap::const_iterator e = range.first; e != range.second; ++e) {
      allowNumber = false;
      findMatch(answer + " " + e->second, line.substr(e->first.length(), line.length()), dic, true, answers);
    }
  }

  if (allowNumber)
    findMatch(answer + " " + line[0], line.substr(1, line.length()), dic, false, answers);
}

bool readDic(DicMap& dic, const string& dicfile) {
  ifstream in(dicfile.c_str());
  if (!in) return false;
  string line;
  while (!in.eof()) {
    getline(in, line);

    string number = line;
    number.erase(remove_if(number.begin(), number.end(), not1(ptr_fun(::isalpha))), number.end());
    transform(number.begin(), number.end(), number.begin(), ::toupper);
    transform(number.begin(), number.end(), number.begin(), toNumber);
    dic.insert(make_pair(number, line));
  }
  return true;
}

int main(int argc, char* argv[]) {
  DicMap dic;
  if (!readDic(dic, argv[1])) return 1;

  ifstream in(argv[2]);
  if (!in) return 1;
  string line;
  while (!in.eof()) {
    getline(in, line);
    string line_real = line;
    line_real.erase( remove_if(line_real.begin(), line_real.end(), not1(ptr_fun(::isdigit))), line_real.end());
    Answers answers;
    findMatch("", line_real, dic, true, answers);
    for (Answers::iterator i = answers.begin(); i != answers.end(); ++i)
      cout << line << ":" << *i << endl;
  }
}

Python code

import string
import sys

letter2digit = "E", "JNQ", "RWX", "DSY", "FT", "AM", "CIV", "BKU", "LOP", "GHZ"

def toNumber(letter):
    for i in range(len(letter2digit)):
        if letter in letter2digit[i]:
            return chr(ord('0') + i)

def findMatch(answer, line, dic, allowNumber, answers):
    if not line:
        answers.append(answer)
        return

    for i in range(1, len(line) + 1):
        if dic.has_key(line[1]):
            allowNumber = False
            for e in dic[line[2]]:
                findMatch(answer + ' ' + e, line[3], dic, True, answers)
    
    if allowNumber:
        findMatch(answer + ' ' + line[0], line[4], dic, False, answers)

def readDic(dicfile):
    dic = { }
    for line in file(dicfile):
        line = line.strip()
        number = filter(lambda x: x in string.ascii_letters, line).upper()
        number = "".join(map(toNumber, number))
        dic[number] = dic.get(number, []) + [line]
    return dic

def main():
    dic = readDic(sys.argv[1])
    for line in file(sys.argv[2]):
        line = line.strip()
        line_real = filter(lambda x: x in string.digits, line)
        answers = []
        findMatch("", line_real, dic, True, answers)
        for answer in answers:
            print "%s:%s" % (line, answer)
    
main()

External Links

• http://www.ipd.uka.de/~prechelt/phonecode/ has the full task description for these examples along with input and output files.

Referenced By