encoding error in python 27

[Hala Gamal]

my code works well with english file but when i use text file encodede"utf-8" "my file contain some arabic letters" it doesn't work.
my code:
# encoding: utf-8
from whoosh import fields, index
import os.path
import re,string
import codecs
from whoosh.qparser import QueryParser

# This list associates a name with each position in a row
columns = ["juza","chapter","verse","voc"]

schema = fields.Schema(juza=fields.NUMERIC(stored=True),
                       chapter=fields.NUMERIC(stored=True),
                       verse=fields.NUMERIC(stored=True),
                       voc=fields.TEXT(stored=True))

# Create the Whoosh index
indexname = "indexdir"
if not os.path.exists(indexname):
  os.mkdir(indexname)
ix = index.create_in(indexname, schema)

# Open a writer for the index
with ix.writer() as writer:
  with codecs.open("tt.txt",encoding='utf-8') as txtfile:
    lines=txtfile.readlines()

    # Read each row in the file
    for i in lines:

      # Create a dictionary to hold the document values for this row
      doc = {}
      thisline=i.split()
      u=0

      # Read the values for the row enumerated like
      # (0, "juza"), (1, "chapter"), etc.
      for w in thisline: 
        # Get the field name from the "columns" list
          fieldname = columns[u]
          u+=1
          #if isinstance(w, basestring):
               #w = unicode(w)
          doc[fieldname] = w
      # Pass the dictionary to the add_document method
      writer.add_document(**doc)
with ix.searcher() as searcher:
    query = QueryParser("voc", ix.schema).parse(u"كتاب")
    results = searcher.search(query)
    print(len(results))
    print(results[1])
my error:
Traceback (most recent call last):
  File "D:\Python27\yarab (4).py", line 45, in <module>
    writer.add_document(**doc)
  File "build\bdist.win32\egg\whoosh\filedb\filewriting.py", line 369, in add_document
    items = field.index(value)
  File "build\bdist.win32\egg\whoosh\fields.py", line 466, in index
    return [(txt, 1, 1.0, '') for txt in self._tiers(num)]
  File "build\bdist.win32\egg\whoosh\fields.py", line 454, in _tiers
    yield self.to_text(num, shift=shift)
  File "build\bdist.win32\egg\whoosh\fields.py", line 487, in to_text
    return self._to_text(self.prepare_number(x), shift=shift,
  File "build\bdist.win32\egg\whoosh\fields.py", line 476, in prepare_number
    x = self.type(x)
UnicodeEncodeError: 'decimal' codec can't encode character u'\ufeff' in position 0: invalid decimal Unicode string
 **my file:
2 2 3 كتاب
2 2 1 لعبة
1 1 1 كتاب
**any help?