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

def Visit_simple_stmt(self, node):  # pylint: disable=invalid-name
    self.DefaultNodeVisit(node)
    if pytree_utils.NodeName(node.children[0]) == 'COMMENT':
      self.last_comment_lineno = node.children[0].lineno

def _SetBlankLinesBetweenCommentAndClassFunc(self, node):
    """Set the number of blanks between a comment and class or func definition.

    Class and function definitions have leading comments as children of the
    classdef and functdef nodes.

    Arguments:
      node: (pytree.Node) The classdef or funcdef node.

    Returns:
      The index of the first child past the comment nodes.
    """
    index = 0
    while pytree_utils.IsCommentStatement(node.children[index]):
      # Standalone comments are wrapped in a simple_stmt node with the comment
      # node as its only child.
      self.Visit(node.children[index].children[0])
      if not self.last_was_decorator:
        self._SetNumNewlines(node.children[index].children[0], _ONE_BLANK_LINE)
      index += 1
    if (index and node.children[index].lineno -
        1 == node.children[index - 1].children[0].lineno):
      self._SetNumNewlines(node.children[index], _NO_BLANK_LINES)
    else:
      if self.last_comment_lineno + 1 == node.children[index].lineno:
        num_newlines = _NO_BLANK_LINES
      else:
        num_newlines = self._GetNumNewlines(node)
      self._SetNumNewlines(node.children[index], num_newlines)
    return index

def _FindStmtParent(node):
  """Find the nearest parent of node that is a statement node.

  Arguments:
    node: node to start from

  Returns:
    Nearest parent (or node itself, if suitable).
  """
  if pytree_utils.NodeName(node) in _STATEMENT_NODES:
    return node
  else:
    return _FindStmtParent(node.parent)

A child_indent annotation on a node specifies the indentation (as a string,
  like "  ") of its children. It is inferred from the INDENT child of a node.

  Arguments:
    tree: root of a pytree. The pytree is modified to add annotations to nodes.

  Raises:
    RuntimeError: if the tree is malformed.
  """
  # Annotate the root of the tree with zero indent.
  if tree.parent is None:
    pytree_utils.SetNodeAnnotation(tree, pytree_utils.Annotation.CHILD_INDENT,
                                   '')
  for child in tree.children:
    if child.type == token.INDENT:
      child_indent = pytree_utils.GetNodeAnnotation(
          tree, pytree_utils.Annotation.CHILD_INDENT)
      if child_indent is not None and child_indent != child.value:
        raise RuntimeError('inconsistent indentation for child', (tree, child))
      pytree_utils.SetNodeAnnotation(tree, pytree_utils.Annotation.CHILD_INDENT,
                                     child.value)
    _AnnotateIndents(child)

previous to this line.
    final_lines: (list of unwrapped_line.UnwrappedLine) The unwrapped lines
      that have already been processed.
    first_nested: (boolean) Whether this is the first nested class or function.

  Returns:
    The number of newlines needed before the first token.
  """
  # TODO(morbo): Special handling for imports.
  # TODO(morbo): Create a knob that can tune these.
  if prev_uwline is None:
    # The first line in the file. Don't add blank lines.
    # FIXME(morbo): Is this correct?
    if first_token.newlines is not None:
      pytree_utils.SetNodeAnnotation(first_token.node,
                                     pytree_utils.Annotation.NEWLINES, None)
    return 0

  if first_token.is_docstring:
    if (prev_uwline.first.value == 'class' and
        style.Get('BLANK_LINE_BEFORE_CLASS_DOCSTRING')):
      # Enforce a blank line before a class's docstring.
      return ONE_BLANK_LINE
    elif (prev_uwline.first.value.startswith('#') and
          style.Get('BLANK_LINE_BEFORE_MODULE_DOCSTRING')):
      # Enforce a blank line before a module's docstring.
      return ONE_BLANK_LINE
    # The docstring shouldn't have a newline before it.
    return NO_BLANK_LINES

  prev_last_token = prev_uwline.last
  if prev_last_token.is_docstring:

def OpensScope(self):
    return self.value in pytree_utils.OPENING_BRACKETS

# Mopping up the prefix is important because we may go over this same
          # child in the next iteration...
          child_prefix = child.prefix.lstrip('\n')
          prefix_indent = child_prefix[:child_prefix.find('#')]
          if '\n' in prefix_indent:
            prefix_indent = prefix_indent[prefix_indent.rfind('\n') + 1:]
          child.prefix = ''

          if child.type == token.NEWLINE:
            # If the prefix was on a NEWLINE leaf, it's part of the line so it
            # will be inserted after the previously encountered leaf.
            # We can't just insert it before the NEWLINE node, because as a
            # result of the way pytrees are organized, this node can be under
            # an inappropriate parent.
            comment_column -= len(comment_prefix.lstrip())
            pytree_utils.InsertNodesAfter(
                _CreateCommentsFromPrefix(
                    comment_prefix,
                    comment_lineno,
                    comment_column,
                    standalone=False), prev_leaf[0])
          elif child.type == token.DEDENT:
            # Comment prefixes on DEDENT nodes also deserve special treatment,
            # because their final placement depends on their prefix.
            # We'll look for an ancestor of this child with a matching
            # indentation, and insert the comment before it if the ancestor is
            # on a DEDENT node and after it otherwise.
            #
            # lib2to3 places comments that should be separated into the same
            # DEDENT node. For example, "comment 1" and "comment 2" will be
            # combined.
            #

lval = left.value
  rval = right.value
  if (left.is_pseudo_paren and _IsIdNumberStringToken(right) and
      left.previous_token and _IsIdNumberStringToken(left.previous_token)):
    # Space between keyword... tokens and pseudo parens.
    return True
  if left.is_pseudo_paren or right.is_pseudo_paren:
    # There should be a space after the ':' in a dictionary.
    if left.OpensScope():
      return True
    # The closing pseudo-paren shouldn't affect spacing.
    return False
  if left.is_continuation or right.is_continuation:
    # The continuation node's value has all of the spaces it needs.
    return False
  if right.name in pytree_utils.NONSEMANTIC_TOKENS:
    # No space before a non-semantic token.
    return False
  if _IsIdNumberStringToken(left) and _IsIdNumberStringToken(right):
    # Spaces between keyword, string, number, and identifier tokens.
    return True
  if lval == ',' and rval == ':':
    # We do want a space between a comma and colon.
    return True
  if rval in ':,':
    # Otherwise, we never want a space before a colon or comma.
    return False
  if lval == ',' and rval in ']})':
    # Add a space between ending ',' and closing bracket if requested.
    return style.Get('SPACE_BETWEEN_ENDING_COMMA_AND_CLOSING_BRACKET')
  if lval == ',':
    # We want a space after a comma.