_yaml: Cythonize and internalize Node

Node used to be a NamedTuple that we used to access by index
for speed reasons. Moving to an extension class allows us to
access attributes by name, making the code easier to read and
less error prone. Moreover, we do gain speed and memory by
doing this move.

Also fix a few places where we would not have an entire `Node`
object but were instead just returning a tuple, missing some entries.

4 files changed, 172 insertions, 159 deletions

diff --git a/.pylintrc b/.pylintrc
index 0dc625a46..e0941862f 100644
--- a/.pylintrc
+++ b/.pylintrc
@@ -3,7 +3,7 @@
 # A comma-separated list of package or module names from where C extensions may
 # be loaded. Extensions are loading into the active Python interpreter and may
 # run arbitrary code
-extension-pkg-whitelist=buildstream._variables
+extension-pkg-whitelist=buildstream._variables,buildstream._yaml
 
 # Add files or directories to the blacklist. They should be base names, not
 # paths.
diff --git a/setup.py b/setup.py
index 90aa74d31..b848e2458 100755
--- a/setup.py
+++ b/setup.py
@@ -391,6 +391,7 @@ def register_cython_module(module_name, dependencies=None):
 
 BUILD_EXTENSIONS = []
 
+register_cython_module("buildstream._yaml")
 register_cython_module("buildstream._variables")
 
 #####################################################
diff --git a/src/buildstream/_yaml.py b/src/buildstream/_yaml.pyx
index cdab4269e..012400d2b 100644
--- a/src/buildstream/_yaml.py
+++ b/src/buildstream/_yaml.pyx
@@ -19,11 +19,12 @@
 #        Tristan Van Berkom <tristan.vanberkom@codethink.co.uk>
 #        Daniel Silverstone <daniel.silverstone@codethink.co.uk>
 #        James Ennis <james.ennis@codethink.co.uk>
+#        Benjamin Schubert <bschubert@bloomberg.net>
 
 import sys
 import string
 from contextlib import ExitStack
-from collections import OrderedDict, namedtuple
+from collections import OrderedDict
 from collections.abc import Mapping, Sequence
 from copy import deepcopy
 from itertools import count
@@ -55,29 +56,36 @@ from ._exceptions import LoadError, LoadErrorReason
 #   line (int): The line number within the file where the value appears.
 #   col (int): The column number within the file where the value appears.
 #
-# For efficiency, each field should be accessed by its integer index:
-#   value = Node[0]
-#   file_index = Node[1]
-#   line = Node[2]
-#   column = Node[3]
-#
-class Node(namedtuple('Node', ['value', 'file_index', 'line', 'column'])):
+cdef class Node:
+
+    cdef public object value
+    cdef public int file_index
+    cdef public int line
+    cdef public int column
+
+    def __init__(self, object value, int file_index, int line, int column):
+        self.value = value
+        self.file_index = file_index
+        self.line = line
+        self.column = column
+
     def __contains__(self, what):
         # Delegate to the inner value, though this will likely not work
         # very well if the node is a list or string, it's unlikely that
         # code which has access to such nodes would do this.
-        return what in self[0]
-
+        return what in self.value
 
 # File name handling
 _FILE_LIST = []
 
 
-# Purely synthetic node will have None for the file number, have line number
+# Purely synthetic node will have _SYNCTHETIC_FILE_INDEX for the file number, have line number
 # zero, and a negative column number which comes from inverting the next value
 # out of this counter.  Synthetic nodes created with a reference node will
 # have a file number from the reference node, some unknown line number, and
 # a negative column number from this counter.
+cdef int _SYNTHETIC_FILE_INDEX = -1
+
 _SYNTHETIC_COUNTER = count(start=-1, step=-1)
 
 
@@ -98,7 +106,7 @@ class ProvenanceInformation:
 
     def __init__(self, nodeish):
         self.node = nodeish
-        if (nodeish is None) or (nodeish[1] is None):
+        if (nodeish is None) or (nodeish.file_index is None):
             self.filename = ""
             self.shortname = ""
             self.displayname = ""
@@ -107,13 +115,13 @@ class ProvenanceInformation:
             self.toplevel = None
             self.project = None
         else:
-            fileinfo = _FILE_LIST[nodeish[1]]
+            fileinfo = _FILE_LIST[nodeish.file_index]
             self.filename = fileinfo[0]
             self.shortname = fileinfo[1]
             self.displayname = fileinfo[2]
             # We add 1 here to convert from computerish to humanish
-            self.line = nodeish[2] + 1
-            self.col = nodeish[3]
+            self.line = nodeish.line + 1
+            self.col = nodeish.column
             self.toplevel = fileinfo[3]
             self.project = fileinfo[4]
         self.is_synthetic = (self.filename == '') or (self.col < 0)
@@ -226,14 +234,14 @@ class Representer:
 
     def _handle_wait_value_ScalarEvent(self, ev):
         key = self.keys.pop()
-        self.output[-1][0][key] = \
+        self.output[-1].value[key] = \
             Node(ev.value, self._file_index, ev.start_mark.line, ev.start_mark.column)
         return "wait_key"
 
     def _handle_wait_value_MappingStartEvent(self, ev):
         new_state = self._handle_doc_MappingStartEvent(ev)
         key = self.keys.pop()
-        self.output[-2][0][key] = self.output[-1]
+        self.output[-2].value[key] = self.output[-1]
         return new_state
 
     def _handle_wait_key_MappingEndEvent(self, ev):
@@ -241,7 +249,7 @@ class Representer:
         # unless it's the last one in which case we leave it
         if len(self.output) > 1:
             self.output.pop()
-            if type(self.output[-1][0]) is list:
+            if type(self.output[-1].value) is list:
                 return "wait_list_item"
             else:
                 return "wait_key"
@@ -250,13 +258,13 @@ class Representer:
 
     def _handle_wait_value_SequenceStartEvent(self, ev):
         self.output.append(Node([], self._file_index, ev.start_mark.line, ev.start_mark.column))
-        self.output[-2][0][self.keys[-1]] = self.output[-1]
+        self.output[-2].value[self.keys[-1]] = self.output[-1]
         return "wait_list_item"
 
     def _handle_wait_list_item_SequenceStartEvent(self, ev):
-        self.keys.append(len(self.output[-1][0]))
+        self.keys.append(len(self.output[-1].value))
         self.output.append(Node([], self._file_index, ev.start_mark.line, ev.start_mark.column))
-        self.output[-2][0].append(self.output[-1])
+        self.output[-2].value.append(self.output[-1])
         return "wait_list_item"
 
     def _handle_wait_list_item_SequenceEndEvent(self, ev):
@@ -271,13 +279,13 @@ class Representer:
             return "wait_key"
 
     def _handle_wait_list_item_ScalarEvent(self, ev):
-        self.output[-1][0].append(
+        self.output[-1].value.append(
             Node(ev.value, self._file_index, ev.start_mark.line, ev.start_mark.column))
         return "wait_list_item"
 
     def _handle_wait_list_item_MappingStartEvent(self, ev):
         new_state = self._handle_doc_MappingStartEvent(ev)
-        self.output[-2][0].append(self.output[-1])
+        self.output[-2].value.append(self.output[-1])
         return new_state
 
     def _handle_doc_DocumentEndEvent(self, ev):
@@ -337,7 +345,7 @@ def load(filename, shortname=None, copy_tree=False, *, project=None):
 
 # Like load(), but doesnt require the data to be in a file
 #
-def load_data(data, file_index=None, file_name=None, copy_tree=False):
+def load_data(data, file_index=_SYNTHETIC_FILE_INDEX, file_name=None, copy_tree=False):
 
     try:
         rep = Representer(file_index)
@@ -351,7 +359,7 @@ def load_data(data, file_index=None, file_name=None, copy_tree=False):
         raise LoadError(LoadErrorReason.INVALID_YAML,
                         "Severely malformed YAML:\n\n{}\n\n".format(e)) from e
 
-    if not isinstance(contents, tuple) or not isinstance(contents[0], dict):
+    if type(contents) != Node:
         # Special case allowance for None, when the loaded file has only comments in it.
         if contents is None:
             contents = Node({}, file_index, 0, 0)
@@ -409,11 +417,11 @@ def node_get_provenance(node, key=None, indices=None):
         return ProvenanceInformation(node)
 
     if key and not indices:
-        return ProvenanceInformation(node[0].get(key))
+        return ProvenanceInformation(node.value.get(key))
 
-    nodeish = node[0].get(key)
+    nodeish = node.value.get(key)
     for idx in indices:
-        nodeish = nodeish[0][idx]
+        nodeish = nodeish.value[idx]
 
     return ProvenanceInformation(nodeish)
 
@@ -451,45 +459,45 @@ def node_get(node, expected_type, key, indices=None, *, default_value=_sentinel,
 
     if indices is None:
         if default_value is _sentinel:
-            value = node[0].get(key, Node(default_value, None, 0, 0))
+            value = node.value.get(key, Node(default_value, _SYNTHETIC_FILE_INDEX, 0, 0))
         else:
-            value = node[0].get(key, Node(default_value, None, 0, next(_SYNTHETIC_COUNTER)))
+            value = node.value.get(key, Node(default_value, _SYNTHETIC_FILE_INDEX, 0, next(_SYNTHETIC_COUNTER)))
 
-        if value[0] is _sentinel:
+        if value.value is _sentinel:
             provenance = node_get_provenance(node)
             raise LoadError(LoadErrorReason.INVALID_DATA,
                             "{}: Dictionary did not contain expected key '{}'".format(provenance, key))
     else:
         # Implied type check of the element itself
         # No need to synthesise useful node content as we destructure it immediately
-        value = Node(node_get(node, list, key), None, 0, 0)
+        value = Node(node_get(node, list, key), _SYNTHETIC_FILE_INDEX, 0, 0)
         for index in indices:
-            value = value[0][index]
+            value = value.value[index]
             if type(value) is not Node:
-                value = (value,)
+                value = Node(value, _SYNTHETIC_FILE_INDEX, 0, 0)
 
     # Optionally allow None as a valid value for any type
-    if value[0] is None and (allow_none or default_value is None):
+    if value.value is None and (allow_none or default_value is None):
         return None
 
-    if (expected_type is not None) and (not isinstance(value[0], expected_type)):
+    if (expected_type is not None) and (not isinstance(value.value, expected_type)):
         # Attempt basic conversions if possible, typically we want to
         # be able to specify numeric values and convert them to strings,
         # but we dont want to try converting dicts/lists
         try:
-            if (expected_type == bool and isinstance(value[0], str)):
+            if (expected_type == bool and isinstance(value.value, str)):
                 # Dont coerce booleans to string, this makes "False" strings evaluate to True
                 # We don't structure into full nodes since there's no need.
-                if value[0] in ('True', 'true'):
-                    value = (True, None, 0, 0)
-                elif value[0] in ('False', 'false'):
-                    value = (False, None, 0, 0)
+                if value.value in ('True', 'true'):
+                    value = Node(True, _SYNTHETIC_FILE_INDEX, 0, 0)
+                elif value.value in ('False', 'false'):
+                    value = Node(False, _SYNTHETIC_FILE_INDEX, 0, 0)
                 else:
                     raise ValueError()
             elif not (expected_type == list or
                       expected_type == dict or
-                      isinstance(value[0], (list, dict))):
-                value = (expected_type(value[0]), None, 0, 0)
+                      isinstance(value.value, (list, dict))):
+                value = Node(expected_type(value.value), _SYNTHETIC_FILE_INDEX, 0, 0)
             else:
                 raise ValueError()
         except (ValueError, TypeError):
@@ -505,8 +513,8 @@ def node_get(node, expected_type, key, indices=None, *, default_value=_sentinel,
                             .format(provenance, path, expected_type.__name__))
 
     # Now collapse lists, and scalars, to their value, leaving nodes as-is
-    if type(value[0]) is not dict:
-        value = value[0]
+    if type(value.value) is not dict:
+        value = value.value
 
     # Trim it at the bud, let all loaded strings from yaml be stripped of whitespace
     if type(value) is str:
@@ -524,13 +532,13 @@ def __trim_list_provenance(value):
     ret = []
     for entry in value:
         if type(entry) is not Node:
-            entry = (entry, None, 0, 0)
-        if type(entry[0]) is list:
-            ret.append(__trim_list_provenance(entry[0]))
-        elif type(entry[0]) is dict:
+            entry = Node(entry, _SYNTHETIC_FILE_INDEX, 0, 0)
+        if type(entry.value) is list:
+            ret.append(__trim_list_provenance(entry.value))
+        elif type(entry.value) is dict:
             ret.append(entry)
         else:
-            ret.append(entry[0])
+            ret.append(entry.value)
     return ret
 
 
@@ -549,22 +557,22 @@ def __trim_list_provenance(value):
 #
 def node_set(node, key, value, indices=None):
     if indices:
-        node = node[0][key]
+        node = node.value[key]
         key = indices.pop()
         for idx in indices:
-            node = node[0][idx]
+            node = node.value[idx]
     if type(value) is Node:
-        node[0][key] = value
+        node.value[key] = value
     else:
         try:
             # Need to do this just in case we're modifying a list
-            old_value = node[0][key]
+            old_value = node.value[key]
         except KeyError:
             old_value = None
         if old_value is None:
-            node[0][key] = Node(value, node[1], node[2], next(_SYNTHETIC_COUNTER))
+            node.value[key] = Node(value, node.file_index, node.line, next(_SYNTHETIC_COUNTER))
         else:
-            node[0][key] = Node(value, old_value[1], old_value[2], old_value[3])
+            node.value[key] = Node(value, old_value.file_index, old_value.line, old_value.column)
 
 
 # node_extend_list()
@@ -585,20 +593,20 @@ def node_set(node, key, value, indices=None):
 def node_extend_list(node, key, length, default):
     assert type(default) is str or default in ([], {})
 
-    list_node = node[0].get(key)
+    list_node = node.value.get(key)
     if list_node is None:
-        list_node = node[0][key] = Node([], node[1], node[2], next(_SYNTHETIC_COUNTER))
+        list_node = node.value[key] = Node([], node.file_index, node.line, next(_SYNTHETIC_COUNTER))
 
-    assert type(list_node[0]) is list
+    assert type(list_node.value) is list
 
-    the_list = list_node[0]
+    the_list = list_node.value
     def_type = type(default)
 
-    file_index = node[1]
+    file_index = node.file_index
     if the_list:
         line_num = the_list[-1][2]
     else:
-        line_num = list_node[2]
+        line_num = list_node.line
 
     while length > len(the_list):
         if def_type is str:
@@ -627,16 +635,16 @@ def node_extend_list(node, key, length, default):
 #
 def node_items(node):
     if type(node) is not Node:
-        node = Node(node, None, 0, 0)
-    for key, value in node[0].items():
+        node = Node(node, _SYNTHETIC_FILE_INDEX, 0, 0)
+    for key, value in node.value.items():
         if type(value) is not Node:
-            value = Node(value, None, 0, 0)
-        if type(value[0]) is dict:
+            value = Node(value, _SYNTHETIC_FILE_INDEX, 0, 0)
+        if type(value.value) is dict:
             yield (key, value)
-        elif type(value[0]) is list:
-            yield (key, __trim_list_provenance(value[0]))
+        elif type(value.value) is list:
+            yield (key, __trim_list_provenance(value.value))
         else:
-            yield (key, value[0])
+            yield (key, value.value)
 
 
 # node_keys()
@@ -652,8 +660,8 @@ def node_items(node):
 #
 def node_keys(node):
     if type(node) is not Node:
-        node = Node(node, None, 0, 0)
-    yield from node[0].keys()
+        node = Node(node, _SYNTHETIC_FILE_INDEX, 0, 0)
+    yield from node.value.keys()
 
 
 # node_del()
@@ -668,7 +676,7 @@ def node_keys(node):
 #
 def node_del(node, key, safe=False):
     try:
-        del node[0][key]
+        del node.value[key]
     except KeyError:
         if not safe:
             raise
@@ -689,7 +697,7 @@ def node_del(node, key, safe=False):
 def is_node(maybenode):
     # It's a programming error to give this a Node which isn't a mapping
     # so assert that.
-    assert (type(maybenode) is not Node) or (type(maybenode[0]) is dict)
+    assert (type(maybenode) is not Node) or (type(maybenode.value) is dict)
     # Now return the type check
     return type(maybenode) is Node
 
@@ -729,9 +737,9 @@ def new_synthetic_file(filename, project=None):
 #
 def new_empty_node(ref_node=None):
     if ref_node is not None:
-        return Node({}, ref_node[1], ref_node[2], next(_SYNTHETIC_COUNTER))
+        return Node({}, ref_node.file_index, ref_node.line, next(_SYNTHETIC_COUNTER))
     else:
-        return Node({}, None, 0, 0)
+        return Node({}, _SYNTHETIC_FILE_INDEX, 0, 0)
 
 
 # new_node_from_dict()
@@ -751,8 +759,8 @@ def new_node_from_dict(indict):
         elif vtype is list:
             ret[k] = __new_node_from_list(v)
         else:
-            ret[k] = Node(str(v), None, 0, next(_SYNTHETIC_COUNTER))
-    return Node(ret, None, 0, next(_SYNTHETIC_COUNTER))
+            ret[k] = Node(str(v), _SYNTHETIC_FILE_INDEX, 0, next(_SYNTHETIC_COUNTER))
+    return Node(ret, _SYNTHETIC_FILE_INDEX, 0, next(_SYNTHETIC_COUNTER))
 
 
 # Internal function to help new_node_from_dict() to handle lists
@@ -765,8 +773,8 @@ def __new_node_from_list(inlist):
         elif vtype is list:
             ret.append(__new_node_from_list(v))
         else:
-            ret.append(Node(str(v), None, 0, next(_SYNTHETIC_COUNTER)))
-    return Node(ret, None, 0, next(_SYNTHETIC_COUNTER))
+            ret.append(Node(str(v), _SYNTHETIC_FILE_INDEX, 0, next(_SYNTHETIC_COUNTER)))
+    return Node(ret, _SYNTHETIC_FILE_INDEX, 0, next(_SYNTHETIC_COUNTER))
 
 
 # _is_composite_list
@@ -787,7 +795,7 @@ def __new_node_from_list(inlist):
 #
 def _is_composite_list(node):
 
-    if type(node[0]) is dict:
+    if type(node.value) is dict:
         has_directives = False
         has_keys = False
 
@@ -817,35 +825,35 @@ def _is_composite_list(node):
 #    source (Node): A composite list
 #
 def _compose_composite_list(target, source):
-    clobber = source[0].get("(=)")
-    prefix = source[0].get("(<)")
-    suffix = source[0].get("(>)")
+    clobber = source.value.get("(=)")
+    prefix = source.value.get("(<)")
+    suffix = source.value.get("(>)")
     if clobber is not None:
         # We want to clobber the target list
         # which basically means replacing the target list
         # with ourselves
-        target[0]["(=)"] = clobber
+        target.value["(=)"] = clobber
         if prefix is not None:
-            target[0]["(<)"] = prefix
-        elif "(<)" in target[0]:
-            target[0]["(<)"][0].clear()
+            target.value["(<)"] = prefix
+        elif "(<)" in target.value:
+            target.value["(<)"].value.clear()
         if suffix is not None:
-            target[0]["(>)"] = suffix
-        elif "(>)" in target[0]:
-            target[0]["(>)"][0].clear()
+            target.value["(>)"] = suffix
+        elif "(>)" in target.value:
+            target.value["(>)"].value.clear()
     else:
         # Not clobbering, so prefix the prefix and suffix the suffix
         if prefix is not None:
-            if "(<)" in target[0]:
-                for v in reversed(prefix[0]):
-                    target[0]["(<)"][0].insert(0, v)
+            if "(<)" in target.value:
+                for v in reversed(prefix.value):
+                    target.value["(<)"].value.insert(0, v)
             else:
-                target[0]["(<)"] = prefix
+                target.value["(<)"] = prefix
         if suffix is not None:
-            if "(>)" in target[0]:
-                target[0]["(>)"][0].extend(suffix[0])
+            if "(>)" in target.value:
+                target.value["(>)"].value.extend(suffix.value)
             else:
-                target[0]["(>)"] = suffix
+                target.value["(>)"] = suffix
 
 
 # _compose_list()
@@ -858,17 +866,17 @@ def _compose_composite_list(target, source):
 #    source (Node): The composition list to be composed from
 #
 def _compose_list(target, source):
-    clobber = source[0].get("(=)")
-    prefix = source[0].get("(<)")
-    suffix = source[0].get("(>)")
+    clobber = source.value.get("(=)")
+    prefix = source.value.get("(<)")
+    suffix = source.value.get("(>)")
     if clobber is not None:
-        target[0].clear()
-        target[0].extend(clobber[0])
+        target.value.clear()
+        target.value.extend(clobber.value)
     if prefix is not None:
-        for v in reversed(prefix[0]):
-            target[0].insert(0, v)
+        for v in reversed(prefix.value):
+            target.value.insert(0, v)
     if suffix is not None:
-        target[0].extend(suffix[0])
+        target.value.extend(suffix.value)
 
 
 # composite_dict()
@@ -885,13 +893,13 @@ def _compose_list(target, source):
 def composite_dict(target, source, path=None):
     if path is None:
         path = []
-    for k, v in source[0].items():
+    for k, v in source.value.items():
         path.append(k)
-        if type(v[0]) is list:
+        if type(v.value) is list:
             # List clobbers anything list-like
-            target_value = target[0].get(k)
+            target_value = target.value.get(k)
             if not (target_value is None or
-                    type(target_value[0]) is list or
+                    type(target_value.value) is list or
                     _is_composite_list(target_value)):
                 raise CompositeError(path,
                                      "{}: List cannot overwrite {} at: {}"
@@ -899,51 +907,51 @@ def composite_dict(target, source, path=None):
                                              k,
                                              node_get_provenance(target, k)))
             # Looks good, clobber it
-            target[0][k] = v
+            target.value[k] = v
         elif _is_composite_list(v):
-            if k not in target[0]:
+            if k not in target.value:
                 # Composite list clobbers empty space
-                target[0][k] = v
-            elif type(target[0][k][0]) is list:
+                target.value[k] = v
+            elif type(target.value[k].value) is list:
                 # Composite list composes into a list
-                _compose_list(target[0][k], v)
-            elif _is_composite_list(target[0][k]):
+                _compose_list(target.value[k], v)
+            elif _is_composite_list(target.value[k]):
                 # Composite list merges into composite list
-                _compose_composite_list(target[0][k], v)
+                _compose_composite_list(target.value[k], v)
             else:
                 # Else composing on top of normal dict or a scalar, so raise...
                 raise CompositeError(path,
                                      "{}: Cannot compose lists onto {}".format(
                                          node_get_provenance(v),
-                                         node_get_provenance(target[0][k])))
-        elif type(v[0]) is dict:
+                                         node_get_provenance(target.value[k])))
+        elif type(v.value) is dict:
             # We're composing a dict into target now
-            if k not in target[0]:
+            if k not in target.value:
                 # Target lacks a dict at that point, make a fresh one with
                 # the same provenance as the incoming dict
-                target[0][k] = Node({}, v[1], v[2], v[3])
-            if type(target[0]) is not dict:
+                target.value[k] = Node({}, v.file_index, v.line, v.column)
+            if type(target.value) is not dict:
                 raise CompositeError(path,
                                      "{}: Cannot compose dictionary onto {}".format(
                                          node_get_provenance(v),
-                                         node_get_provenance(target[0][k])))
-            composite_dict(target[0][k], v, path)
+                                         node_get_provenance(target.value[k])))
+            composite_dict(target.value[k], v, path)
         else:
-            target_value = target[0].get(k)
-            if target_value is not None and type(target_value[0]) is not str:
+            target_value = target.value.get(k)
+            if target_value is not None and type(target_value.value) is not str:
                 raise CompositeError(path,
                                      "{}: Cannot compose scalar on non-scalar at {}".format(
                                          node_get_provenance(v),
-                                         node_get_provenance(target[0][k])))
-            target[0][k] = v
+                                         node_get_provenance(target.value[k])))
+            target.value[k] = v
         path.pop()
 
 
 # Like composite_dict(), but raises an all purpose LoadError for convenience
 #
 def composite(target, source):
-    assert type(source[0]) is dict
-    assert type(target[0]) is dict
+    assert type(source.value) is dict
+    assert type(target.value) is dict
 
     try:
         composite_dict(target, source)
@@ -964,11 +972,11 @@ def composite(target, source):
 def composite_and_move(target, source):
     composite(source, target)
 
-    to_delete = [key for key in target[0].keys() if key not in source[0]]
-    for key, value in source[0].items():
-        target[0][key] = value
+    to_delete = [key for key in target.value.keys() if key not in source.value]
+    for key, value in source.value.items():
+        target.value[key] = value
     for key in to_delete:
-        del target[0][key]
+        del target.value[key]
 
 
 # Types we can short-circuit in node_sanitize for speed.
@@ -987,7 +995,7 @@ def node_sanitize(node, *, dict_type=OrderedDict):
 
     # If we have an unwrappable node, unwrap it
     if node_type is Node:
-        node = node[0]
+        node = node.value
         node_type = type(node)
 
     # Short-circuit None which occurs ca. twice per element
@@ -1039,7 +1047,7 @@ def node_validate(node, valid_keys):
 
     # Probably the fastest way to do this: https://stackoverflow.com/a/23062482
     valid_keys = set(valid_keys)
-    invalid = next((key for key in node[0] if key not in valid_keys), None)
+    invalid = next((key for key in node.value if key not in valid_keys), None)
 
     if invalid:
         provenance = node_get_provenance(node, key=invalid)
@@ -1077,8 +1085,8 @@ __NODE_ASSERT_COMPOSITION_DIRECTIVES = ('(>)', '(<)', '(=)')
 #
 def node_copy(source):
     copy = {}
-    for key, value in source[0].items():
-        value_type = type(value[0])
+    for key, value in source.value.items():
+        value_type = type(value.value)
         if value_type is dict:
             copy[key] = node_copy(value)
         elif value_type is list:
@@ -1088,14 +1096,18 @@ def node_copy(source):
         else:
             raise ValueError("Unable to be quick about node_copy of {}".format(value_type))
 
-    return Node(copy, source[1], source[2], source[3])
+    return Node(copy, source.file_index, source.line, source.column)
 
 
 # Internal function to help node_copy() but for lists.
 def _list_copy(source):
     copy = []
-    for item in source[0]:
-        item_type = type(item[0])
+    for item in source.value:
+        if type(item) is Node:
+            item_type = type(item.value)
+        else:
+            item_type = type(item)
+
         if item_type is dict:
             copy.append(node_copy(item))
         elif item_type is list:
@@ -1105,7 +1117,7 @@ def _list_copy(source):
         else:
             raise ValueError("Unable to be quick about list_copy of {}".format(item_type))
 
-    return Node(copy, source[1], source[2], source[3])
+    return Node(copy, source.file_index, source.line, source.column)
 
 
 # node_final_assertions()
@@ -1122,7 +1134,7 @@ def _list_copy(source):
 def node_final_assertions(node):
     assert type(node) is Node
 
-    for key, value in node[0].items():
+    for key, value in node.value.items():
 
         # Assert that list composition directives dont remain, this
         # indicates that the user intended to override a list which
@@ -1133,7 +1145,7 @@ def node_final_assertions(node):
             raise LoadError(LoadErrorReason.TRAILING_LIST_DIRECTIVE,
                             "{}: Attempt to override non-existing list".format(provenance))
 
-        value_type = type(value[0])
+        value_type = type(value.value)
 
         if value_type is dict:
             node_final_assertions(value)
@@ -1143,8 +1155,8 @@ def node_final_assertions(node):
 
 # Helper function for node_final_assertions(), but for lists.
 def _list_final_assertions(values):
-    for value in values[0]:
-        value_type = type(value[0])
+    for value in values.value:
+        value_type = type(value.value)
 
         if value_type is dict:
             node_final_assertions(value)
@@ -1218,7 +1230,7 @@ def node_find_target(node, target, *, key=None):
     assert type(node) is Node
     assert type(target) is Node
     if key is not None:
-        target = target[0][key]
+        target = target.value[key]
 
     path = []
     if _walk_find_target(node, path, target):
@@ -1231,18 +1243,18 @@ def node_find_target(node, target, *, key=None):
 
 # Helper for node_find_target() which walks a value
 def _walk_find_target(node, path, target):
-    if node[1:] == target[1:]:
+    if node.file_index == target.file_index and node.line == target.line and node.column == target.column:
         return True
-    elif type(node[0]) is dict:
+    elif type(node.value) is dict:
         return _walk_dict_node(node, path, target)
-    elif type(node[0]) is list:
+    elif type(node.value) is list:
         return _walk_list_node(node, path, target)
     return False
 
 
 # Helper for node_find_target() which walks a list
 def _walk_list_node(node, path, target):
-    for i, v in enumerate(node[0]):
+    for i, v in enumerate(node.value):
         path.append(i)
         if _walk_find_target(v, path, target):
             return True
@@ -1252,7 +1264,7 @@ def _walk_list_node(node, path, target):
 
 # Helper for node_find_target() which walks a mapping
 def _walk_dict_node(node, path, target):
-    for k, v in node[0].items():
+    for k, v in node.value.items():
         path.append(k)
         if _walk_find_target(v, path, target):
             return True
diff --git a/tests/internals/yaml.py b/tests/internals/yaml.py
index dae20b326..6b26fdfaf 100644
--- a/tests/internals/yaml.py
+++ b/tests/internals/yaml.py
@@ -22,7 +22,7 @@ def test_load_yaml(datafiles):
                             'basics.yaml')
 
     loaded = _yaml.load(filename)
-    assert loaded[0].get('kind')[0] == 'pony'
+    assert loaded.value.get('kind').value == 'pony'
 
 
 def assert_provenance(filename, line, col, node, key=None, indices=None):
@@ -43,7 +43,7 @@ def test_basic_provenance(datafiles):
                             'basics.yaml')
 
     loaded = _yaml.load(filename)
-    assert loaded[0].get('kind')[0] == 'pony'
+    assert loaded.value.get('kind').value == 'pony'
 
     assert_provenance(filename, 1, 0, loaded)
 
@@ -56,7 +56,7 @@ def test_member_provenance(datafiles):
                             'basics.yaml')
 
     loaded = _yaml.load(filename)
-    assert loaded[0].get('kind')[0] == 'pony'
+    assert loaded.value.get('kind').value == 'pony'
     assert_provenance(filename, 2, 13, loaded, 'description')
 
 
@@ -68,7 +68,7 @@ def test_element_provenance(datafiles):
                             'basics.yaml')
 
     loaded = _yaml.load(filename)
-    assert loaded[0].get('kind')[0] == 'pony'
+    assert loaded.value.get('kind').value == 'pony'
     assert_provenance(filename, 5, 2, loaded, 'moods', [1])
 
 
@@ -102,7 +102,7 @@ def test_node_get(datafiles):
                             'basics.yaml')
 
     base = _yaml.load(filename)
-    assert base[0].get('kind')[0] == 'pony'
+    assert base.value.get('kind').value == 'pony'
 
     children = _yaml.node_get(base, list, 'children')
     assert isinstance(children, list)
@@ -522,9 +522,9 @@ def test_node_find_target(datafiles, case):
     # laid out.  Client code should never do this.
     def _walk(node, entry, rest):
         if rest:
-            return _walk(node[0][entry], rest[0], rest[1:])
+            return _walk(node.value[entry], rest[0], rest[1:])
         else:
-            return node[0][entry]
+            return node.value[entry]
 
     want = _walk(loaded, case[0], case[1:])
     found_path = _yaml.node_find_target(toplevel, want)