from collections.abc import Iterator
from itertools import tee
from typing import Tuple, List, Collection, Dict, Set

def safehash(obj)->int:
  '''
  Tool to take a hash of an object in a safe way.
  The idea is that it intercepts non-hashable types
  and works around it.
  '''
  try:
      # first try the dumb way, because the safe way is expensive
      # see also #357
      return obj.__hash__()
  except TypeError:
      # the constants are to distinguish between the types
      if isinstance(obj, Set): #order irrelevant
          return 17+sum([safehash(it) for it in obj])
      if isinstance(obj, Dict): # order irrelevant. 
          return 133+sum([safehash(item) for item in obj.items() ])
      if isinstance(obj, List) or isinstance(obj, tuple): # order is important
          return 31+hash( tuple ( safehash(elt) for elt in obj ) )
  raise ValueError("Type not yet handled: "+str(obj))