text: import data
  
  import pprint
  ffi=data['ffi']
  
  @ffi.callback('int(int)')
  def func(a):
      print('Python: Got from C %d' % a)
      return a * 2
  
  @ffi.callback('void()')
  def c_callback():
      print('Python: called from c_callback')
  
  def init():
      #add our generic callback...
      data['gl'].callbacks.c_2_pypy_callback = ffi.cast('void *',c_callback)
  
      print("***calling C from pypy***")
      c_func = ffi.cast('int(*)(int(*)(int))',data['gl'].callbacks.pypy_2_c_callback)
      c_func(func)