Python: write.csv adding extra carriage return

I am writing an Excl to CSV converter using python. I'm running in Linux and my Python version is: Python 2.7.1 (r271:86832, Dec 4 2012, 17:16:32) [GCC 4.1.2 20080704 (Red Hat 4.1.2-51)] on linux2

In the code as below, when I comment the 5 "csvFile.write" lines, the csv file is generated all fine. However, with the code as is, a carriage return is getting added at the end of all the lines produced by "wr.writerow".

Question: Why the csv write is adding the extra carriage return when "csvFile.write" are present ?

import sys  # For interacting with the Unix Shell
import os   # For OS information (mainly path manipulation)

import time # For data and time
import xlrd # For reading both XLS/XLSX files
import csv  # Writing CSV files

# Get the Excel file from cmd line arguments
excelFile = sys.argv[1]

def csv_from_excel(excelFile):
  wb = xlrd.open_workbook(excelFile, encoding_override='utf8')
  sh = wb.sheet_by_index(0)
  print sh.name, sh.nrows, sh.ncols
  # Output file
  csvFileName= os.path.splitext(excelFile)[0] + '.csv'  
  # Open file for write
  try:
    csvFile = open(csvFileName, 'wb')
  except IOError:
    print "Error: cannot open output CSV file"
  # Print a header to the output file
  csvFile.write('###########################################################\n')
  csvFile.write('# Python Version: %s\n' % (sys.version))
  csvFile.write('# Date: %s\n' % time.strftime("%d/%m/%Y, %H:%M:%S"))
  csvFile.write('# User: %s\n' % os.getlogin())
  csvFile.write('###########################################################\n\n')
  # Wite Values
  wr = csv.writer(csvFile, delimiter=';')

  for rownum in xrange(sh.nrows):
    wr.writerow([unicode(val).encode('utf8') for val in sh.row_values(rownum)])

  csvFile.close()

if __name__ == "__main__":
  csv_from_excel(excelFile)