#! /usr/bin/env python
# -*- coding: utf-8 -*-

(C) 2005 by Damir Cavar <dcavar@indiana.edu>


This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.


1. Startup:
   Lid loads all *.dat files in the current directory, assuming that
   the files contain the tri-gram model of the language which is named
   with the file name (e.g. japanese.dat, german.dat etc.).

2. Processing:
   Lid processes all the files given as parameters to the script and prints
   out the language of the text that the file contains.

Lid can be used within an application by importing the class and using its
methods as shown in the end of this code (the __main__ part):

myLid = Lid()
languagename = myLid("This is an English example.")


   Lid is based on a tri-gram model of a training corpus for a given language.
   Use lidtrainer.py to generate such language models.

   The language models are sets of three character sequences (tri-grams) extracted
   from the training corpus, with their frequency. The probability of each
   tri-gram is calculated (given the frequency of the tri-gram and the number
   of all tri-grams in the corpus) and stored with the tri-gram in the language

   Lid generates all tri-grams for the test document and compares the probability
   of each tri-gram with the probabilities the corresponding tri-grams in the
   training corpus or the language model. For each tri-gram the deviation from
   the corresponding tri-gram in the language model is calculated. If a tri-gram is
   not found in the language model, the deviation is assumed to be maximal, i.e.
   equal to 1.

   The language model that has the minimal deviation score for the tri-grams in
   the tested text is assumed to represent the language of the tested text.

   This is a very simple but effective language ID strategy. It is developed for
   teaching purposes. A real world application would require much more evaluation
   of the significance of the deviations, optimization of the language models and
   many many other things.

Please send your comments and suggestions!

__version__ = 0.2
__author__ = "Damir Cavar"

import sys, re, os.path, glob
from string import *
from os import listdir, getcwd

class Lid:
   """The basic Language Identification class

   num        = 0  # number of trigrams
   characters = 0  # number of characters
   languages  = [] # list of loaded language models
   models     = [] # list with the trigram models
   trigrams   = {} # trigrams of the analyzed document

   def __init__(self):
      """Lid constructor
         The constructor loads automatically all language models in the
         current directory.
         The language models are stored in files that are made up as follows:
         LANGUAGE_NAME followd by .dat.
      for x in listdir(getcwd()):
         if x[-4:] == ".dat":
            modelfile = file(x)
            self.languages.append(upper(x[0]) + x[1:-4])
            newdict = {}
            for line in modelfile:
               tokens = split(line)
               if len(tokens) == 2:
                  newdict[tokens[0]] = float(tokens[1])
            modelnum = len(self.models)

   def checkText(self, text):
      """Check which language a text is."""
      self.createTrigrams(text) # create trigrams of submitted text
      self.calcProb()           # calculate probabilities

      result = []               # storage for the matches with the models
      for x in range(len(self.languages)):
      # for all keys in trigrams
      for x in self.trigrams.keys():
         # for 0 to number language models
         for i in range(len(self.models)):
            # get the current model
            mymodel = self.models[i]
            if mymodel.has_key(x):
               # if the model contains the key, get the deviation
               value = mymodel[x] - self.trigrams[x]
               if value < 0:
                  value = value * -1
               result[i] += value
               # otherwise set the resulting value to 1 = max. deviation
               result[i] += 1
      value = float(1.0)
      element = 0
      for x in range(len(result)):
         result[x] = float(result[x])/float(self.num)
         if value > result[x]:
            value = float(result[x])
            element = x
      return self.languages[element]

   def createTrigrams(self, text):
      """Creates tri-grams from characters."""
      self.num = 0                    # storage for the number of trigrams
      self.trigrams = {}              # dictionary storage for trigrams
      text = re.sub(r"\n", " ", text) # replace newlines in text
      text = self.cleanTextSC(text)   # clean trigrams with punctuation marks
      text = re.sub(r"\s+", " ", text) # replace multiple spaces/tabs 
      self.characters = len(text)     # get number of characters

      # go thru list up to one but last word and take
      # the actual word and the following word together
      for i in range(len(text) - 2):
         self.num += 1
         self.trigrams[text[i:i+3]] = self.trigrams.get(text[i:i+3], 0) + 1

   def calcProb(self):
      """Calculate the probabilities for each trigram."""
      for x in self.trigrams.keys():
         self.trigrams[x] = float(self.trigrams[x]) / float(self.num)

   def eliminateFrequences(self, num):
      """Eliminates all bigrams with a frequency <= num"""
      for x in self.trigrams.keys():
         if self.trigrams[x] <= num:
            value = self.trigrams[x]
            del self.trigrams[x]
            self.num -= value

   def createTrigramNSC(self, text):
      """Creates bigrams without punctuation symbols."""

   def cleanTextSC(self, text):
      """Eliminates punctuation symbols from the submitted text."""
      for i in punctuation:
         if i in text:
            text = replace(text, i, " ")
      return text

   def cleanPBIG(self):
      """Eliminate tri-grams that contain punctuation marks."""
      for i in self.trigrams.keys():
         for a in punctuation:
            if a in i:
               value = self.trigrams[i]
               del self.trigrams[i]
               self.num -= value

if __name__ == "__main__":
   if len(sys.argv) > 1:
      myLid = Lid()
      for i in sys.argv[1:]:
         for y in glob.glob(os.path.normcase(i)):
               print "File:\t" + str(y) + "\tLanguage:\t" + myLid.checkText(open(y).read())
            except IOError:
               print "Cannot open file:" + str(y)
      print "Usage:"
      print "python Lid.py [filename]"