class_docstr: Node in a tree that corresponds to previous interactions with
  a ``ConjectureData`` object according to some fixed test function.
  
  This is functionally a variant patricia trie.
  See https://en.wikipedia.org/wiki/Radix_tree for the general idea,
  but what this means in particular here is that we have a very deep
  but very lightly branching tree and rather than store this as a fully
  recursive structure we flatten prefixes and long branches into
  lists. This significantly compacts the storage requirements.
  
  A single ``TreeNode`` corresponds to a previously seen sequence
  of calls to ``ConjectureData`` which we have never seen branch,
  followed by a ``transition`` which describes what happens next.
docstr: Note that the value at index ``i`` was forced.
docstr_tok: ["Note","that","the","value","at","index","``","i","``","was","forced","."]
code: def mark_forced(self, i):
      """Note that the value at index ``i`` was forced."""
      assert 0 <= i < len(self.values)
      if self.__forced is None:
          self.__forced = set()
      self.__forced.add(i)
  
imports: import attr
  from hypothesis.errors import Flaky, HypothesisException, StopTest
  from hypothesis.internal.compat import int_to_bytes
  from hypothesis.internal.conjecture.data import ConjectureData, DataObserver, Status, bits_to_bytes
  from hypothesis.internal.conjecture.junkdrawer import IntList
label_desc: Use image node_id 2 for calling the TreeNode obj's underlying member method code with example usage: obj.mark_forced(i) without return types