Getting a root of an arabic word

I have a python code that take an arabic word and get the root and also remove diacretics. but i have a problem with the output. For example : when the input is "العربيه" the output is:"عرب" but when the input is "كاتب" the output is:"ب", and when the input is "يخاف" the output is " خف".

This is my code:

# -*- coding=utf-8 -*-

import re
from arabic_const import *
import Tashaphyne
from Tashaphyne import *
import enum
from enum import Enum
search_type=Enum('unvoc_word','voc_word','root_word')

HARAKAT_pat = re.compile(ur"[" + u"".join([FATHATAN, DAMMATAN, KASRATAN, FATHA, DAMMA, KASRA, SUKUN, SHADDA]) + u"]")
HAMZAT_pat = re.compile(ur"[" + u"".join([WAW_HAMZA, YEH_HAMZA]) + u"]");
ALEFAT_pat = re.compile(ur"[" + u"".join([ALEF_MADDA, ALEF_HAMZA_ABOVE, ALEF_HAMZA_BELOW, HAMZA_ABOVE, HAMZA_BELOW]) + u"]");
LAMALEFAT_pat = re.compile(ur"[" + u"".join([LAM_ALEF, LAM_ALEF_HAMZA_ABOVE, LAM_ALEF_HAMZA_BELOW, LAM_ALEF_MADDA_ABOVE]) + u"]");
#--------------------------------------
def strip_tashkeel(w):
        "strip vowel from a word and return a result word"
        return HARAKAT_pat.sub('', w)

#strip tatweel from a word and return a result word
#--------------------------------------
def strip_tatweel(w):
        "strip tatweel from a word and return a result word"
        return re.sub(ur'[%s]' % TATWEEL,       '', w)


#--------------------------------------
def normalize_hamza(w):
        "strip vowel from a word and return a result word"
        w = ALEFAT_pat.sub(ALEF, w)
        return HAMZAT_pat.sub(HAMZA, w)

#--------------------------------------
def normalize_lamalef(w):
        "strip vowel from a word and return a result word"
        return LAMALEFAT_pat.sub(u'%s%s' % (LAM, ALEF), w)

#--------------------------------------
def normalize_spellerrors(w):
        "strip vowel from a word and return a result word"
        w = re.sub(ur'[%s]' % TEH_MARBUTA,      HEH, w)
        return re.sub(ur'[%s]' % ALEF_MAKSURA,  YEH, w)


def normalize_text(word,searchtype):
        word = strip_tashkeel(word)
        word = strip_tatweel(word)
        word = normalize_lamalef(word)
        word = normalize_hamza(word)
        word = normalize_spellerrors(word)
        if searchtype==search_type.root_word.index:
           ArListem=ArabicLightStemmer();
           stem=ArListem.lightStm(word);
           word=ArListem.get_root();
        print word
        return word
#---------------------------------------------

and this is the test code:

**from task import normalize_text
normalize_text(u'كاتب',2)

and the output is: ب