How to use the yapf.yapflib.pytree_utils.FirstLeafNode function in yapf

def Visit_power(self, node):  # pylint: disable=invalid-name,missing-docstring
    # power ::= atom trailer* ['**' factor]
    self.DefaultNodeVisit(node)

    # When atom is followed by a trailer, we can not break between them.
    # E.g. arr[idx] - no break allowed between 'arr' and '['.
    if (len(node.children) > 1 and
        pytree_utils.NodeName(node.children[1]) == 'trailer'):
      # children[1] itself is a whole trailer: we don't want to
      # mark all of it as unbreakable, only its first token: (, [ or .
      first = pytree_utils.FirstLeafNode(node.children[1])
      if first.value != '.':
        _SetUnbreakable(node.children[1].children[0])

      # A special case when there are more trailers in the sequence. Given:
      #   atom tr1 tr2
      # The last token of tr1 and the first token of tr2 comprise an unbreakable
      # region. For example: foo.bar.baz(1)
      # We can't put breaks between either of the '.', '(', or '[' and the names
      # *preceding* them.
      prev_trailer_idx = 1
      while prev_trailer_idx < len(node.children) - 1:
        cur_trailer_idx = prev_trailer_idx + 1
        cur_trailer = node.children[cur_trailer_idx]
        if pytree_utils.NodeName(cur_trailer) == 'trailer':
          # Now we know we have two trailers one after the other
          prev_trailer = node.children[prev_trailer_idx]

if first == last and first.type == token.COMMENT:
    # A comment was inserted before the value, which is a pytree.Leaf.
    # Encompass the dictionary's value into an ATOM node.
    last = first.next_sibling
    last_clone = last.clone()
    new_node = pytree.Node(syms.atom, [first.clone(), last_clone])
    for orig_leaf, clone_leaf in zip(last.leaves(), last_clone.leaves()):
      pytree_utils.CopyYapfAnnotations(orig_leaf, clone_leaf)
      if hasattr(orig_leaf, 'is_pseudo'):
        clone_leaf.is_pseudo = orig_leaf.is_pseudo

    node.replace(new_node)
    node = new_node
    last.remove()

    first = pytree_utils.FirstLeafNode(node)
    last = pytree_utils.LastLeafNode(node)

  lparen = pytree.Leaf(
      token.LPAR, u'(', context=('', (first.get_lineno(), first.column - 1)))
  last_lineno = last.get_lineno()
  if last.type == token.STRING and '\n' in last.value:
    last_lineno += last.value.count('\n')

  if last.type == token.STRING and '\n' in last.value:
    last_column = len(last.value.split('\n')[-1]) + 1
  else:
    last_column = last.column + len(last.value) + 1
  rparen = pytree.Leaf(
      token.RPAR, u')', context=('', (last_lineno, last_column)))

  lparen.is_pseudo = True

def Visit_subscriptlist(self, node):  # pylint: disable=invalid-name
    # subscriptlist ::= subscript (',' subscript)* [',']
    self.DefaultNodeVisit(node)
    _SetSplitPenalty(pytree_utils.FirstLeafNode(node), 0)
    prev_child = None
    for child in node.children:
      if prev_child and pytree_utils.NodeName(prev_child) == 'COMMA':
        _SetSplitPenalty(pytree_utils.FirstLeafNode(child), 0)
      prev_child = child

def Visit_or_test(self, node):  # pylint: disable=invalid-name
    # or_test ::= and_test ('or' and_test)*
    self.DefaultNodeVisit(node)
    _IncreasePenalty(node, OR_TEST)
    index = 1
    while index + 1 < len(node.children):
      if style.Get('SPLIT_BEFORE_LOGICAL_OPERATOR'):
        _DecrementSplitPenalty(
            pytree_utils.FirstLeafNode(node.children[index]), OR_TEST)
      else:
        _DecrementSplitPenalty(
            pytree_utils.FirstLeafNode(node.children[index + 1]), OR_TEST)
      index += 2

def Visit_subscriptlist(self, node):  # pylint: disable=invalid-name
    # subscriptlist ::= subscript (',' subscript)* [',']
    self.DefaultNodeVisit(node)
    _SetSplitPenalty(pytree_utils.FirstLeafNode(node), 0)
    prev_child = None
    for child in node.children:
      if prev_child and pytree_utils.NodeName(prev_child) == 'COMMA':
        _SetSplitPenalty(pytree_utils.FirstLeafNode(child), 0)
      prev_child = child

def Visit_atom(self, node):  # pylint: disable=invalid-name
    # atom ::= ('(' [yield_expr|testlist_gexp] ')'
    #           '[' [listmaker] ']' |
    #           '{' [dictsetmaker] '}')
    self.DefaultNodeVisit(node)
    if (node.children[0].value == '(' and
        not hasattr(node.children[0], 'is_pseudo')):
      if node.children[-1].value == ')':
        if pytree_utils.NodeName(node.parent) == 'if_stmt':
          _SetSplitPenalty(node.children[-1], STRONGLY_CONNECTED)
        else:
          if len(node.children) > 2:
            _SetSplitPenalty(pytree_utils.FirstLeafNode(node.children[1]), EXPR)
          _SetSplitPenalty(node.children[-1], ATOM)
    elif node.children[0].value in '[{' and len(node.children) == 2:
      # Keep empty containers together if we can.
      _SetUnbreakable(node.children[-1])

def RecExpression(node, first_child_leaf):
    if node is first_child_leaf:
      return

    if isinstance(node, pytree.Leaf):
      if node.value in {'(', 'for'}:
        return
      penalty = pytree_utils.GetNodeAnnotation(
          node, pytree_utils.Annotation.SPLIT_PENALTY, default=0)
      _SetSplitPenalty(node, penalty + amt)
    else:
      for child in node.children:
        RecExpression(child, first_child_leaf)

  RecExpression(node, pytree_utils.FirstLeafNode(node))

def _InsertPseudoParentheses(node):
  """Insert pseudo parentheses so that dicts can be formatted correctly."""
  comment_node = None
  if isinstance(node, pytree.Node):
    if node.children[-1].type == token.COMMENT:
      comment_node = node.children[-1].clone()
      node.children[-1].remove()

  first = pytree_utils.FirstLeafNode(node)
  last = pytree_utils.LastLeafNode(node)

  if first == last and first.type == token.COMMENT:
    # A comment was inserted before the value, which is a pytree.Leaf.
    # Encompass the dictionary's value into an ATOM node.
    last = first.next_sibling
    last_clone = last.clone()
    new_node = pytree.Node(syms.atom, [first.clone(), last_clone])
    for orig_leaf, clone_leaf in zip(last.leaves(), last_clone.leaves()):
      pytree_utils.CopyYapfAnnotations(orig_leaf, clone_leaf)
      if hasattr(orig_leaf, 'is_pseudo'):
        clone_leaf.is_pseudo = orig_leaf.is_pseudo

    node.replace(new_node)
    node = new_node
    last.remove()

def RecExpression(node, first_child_leaf):
    if node is first_child_leaf:
      return

    if isinstance(node, pytree.Leaf):
      if node.value in {'(', 'for', 'if'}:
        return
      penalty_annotation = pytree_utils.GetNodeAnnotation(
          node, pytree_utils.Annotation.SPLIT_PENALTY, default=0)
      if penalty_annotation < penalty:
        _SetSplitPenalty(node, penalty)
    else:
      for child in node.children:
        RecExpression(child, first_child_leaf)

  RecExpression(node, pytree_utils.FirstLeafNode(node))