new_contents: 
  # use time() instead on unix
  import sys
  if sys.platform=='win32':
      from time import clock
  else:
      from time import time as clock
  
  from sympycore import profile_expr
  
  def time1(n=5):
      from sympycore import Symbol, sin
      x,y,z = map(Symbol,'xyz')
      f = (x / (1+sin(x**(y+x**2)))**2)
      t1 = clock()
      while n:
          f = f.diff(x)
          n -= 1
      t2 = clock()
      return 100 / (t2-t1)
  
  def time2(n=5):
      from sympy import Symbol, sin
      x,y,z = map(Symbol,'xyz')
      f = (x / (1+sin(x**(y+x**2)))**2)
      t1 = clock()
      while n:
          f = f.diff(x)
          n -= 1
      t2 = clock()
      #print 'time2:',t2-t1
      return 100 / (t2-t1)
  
  def time3(n=5):
      import swiginac
      x,y,z = map(swiginac.symbol,'xyz')
      f = (x / (1+swiginac.sin(x**(y+x**2)))**2)
      t1 = clock()
      while n:
          f = f.diff(x)
          n -= 1
      t2 = clock()
      print 'time3:',t2-t1
      return 100 / (t2-t1)
  
  def timing():
      t1 = time1()
      t2 = time3()
      return t1, t2, t1/t2
  
  print timing()
  print timing()
  print timing()
  
  profile_expr('time1(5)')
  
subject: Add diff bench test script.