code: def isdag(d, keys):
      """Does graph form a directed acyclic graph when calculating keys? ``keys`` may be a single key or list of keys.
  
      Examples
      --------
      >>> from flash.core.serve.dag.utils_test import inc
      >>> isdag({'x': 0, 'y': (inc, 'x')}, 'y')
      True
      >>> isdag({'x': (inc, 'y'), 'y': (inc, 'x')}, 'y')
      False
  
      See Also
      --------
      getcycle
  
      """
      return not getcycle(d, keys)
  
imports: from collections import defaultdict
  from typing import List, Sequence
  from flash.core.utilities.imports import _TOPIC_SERVE_AVAILABLE
label_desc: Use image node_id 15 for calling a global function with example usage: isdag(d, keys) and returns: unknown