code: def get_function(fn_name):
      
      module_name, callable_name = fn_name.split(':')
      current = globals()
      if not callable_name:
          callable_name = module_name
      else:
          import importlib
          try:
              module = importlib.import_module(module_name)
          except ImportError:
              log.error("failed to import %s", module_name)
              raise
          current = module
      for level in callable_name.split('.'):
          current = getattr(current, level)
      code = current.__code__
      if code.co_argcount != 2:
          raise ValueError('function should take 2 arguments: lines, file_name')
      return current
docs: Retrieve the function defined by the function_name.
  
      Arguments:
        fn_name: specification of the type module:function_name.