new_contents: 
  """
  Wood author: thislight
  
  Copyright 2016 thislight
  
     Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.
     You may obtain a copy of the License at
  
         http://www.apache.org/licenses/LICENSE-2.0
  
     Unless required by applicable law or agreed to in writing, software
     distributed under the License is distributed on an "AS IS" BASIS,
     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     See the License for the specific language governing permissions and
     limitations under the License.
  
  Under License Apache v2, more information, see file 'LICENSE' in project root directory.
  """
  
  import time
  
  
  def timeit(callback=None,num=4):
      """
      A function timer.
      arg callback: a function to rev. time result.
      arg num: ...example: 0.162839, num=4 -> callback('0.1628')
      Return: function
      """
       def timeit(f)
          if not callback: return f
          def mock_func(*args,**kargs):
              t1 = time.process_time()
              _r = f(*args,**kargs)
              t2 = time.process_time()
              template = '{0:.%if}' % num
              callback(template.format(t2-t1))
              return _r
         return mock_func
      return timeit
  
  
subject: ADD timeit util.