code: def has_nested_keys(mapping, k1, *more):
      
      if k1 in mapping:
          if more:
              return has_nested_keys(mapping[k1], *more)
          else:
              return True
      else:
          return False
docs: Return ``True`` if `mapping[k1][k2]...[kN]` is valid.
  
      Example::
  
        >>> D = {
        ...   'a': {
        ...     'x':0,
        ...     'y':{
        ...       'z': 1,
        ...     },
        ...   },
        ...   'b': 3
        ... }
        >>> has_nested_keys(D, 'a', 'x')
        True
        >>> has_nested_keys(D, 'a', 'y', 'z')
        True
        >>> has_nested_keys(D, 'a', 'q')
        False
  
      When a single key is passed, this is just another way of writing ``k1 in
      mapping``::
  
        >>> has_nested_keys(D, 'b')
        True