_yaml.pyx: Forbid expected_type=Mapping, and remove isinstance check

Calls to `isinstance` can be particularily costly. Using type() is
much faster. The only known case where the `isinstance` was useful
is for dictionnaries where we would ask for a 'Mapping' instead.

Disallowing 'Mapping' for expected_type considerably speeds up the
calls to this functions.

Also add into NEWS

11 files changed, 63 insertions, 69 deletions

diff --git a/NEWS b/NEWS
index ee935711e..c37ad1b6a 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,9 @@
 buildstream 1.3.1
 =================
 
+  o BREAKING CHANGE: `node_get_member` doesn't accept 'expected_type=Mapping'
+    anymore. Please use 'expected_type=dict' instead.
+
   o BREAKING CHANGE: Artifact as a Proto. The caching of buildstream artifacts
     has changed from a reference based impelementation. Existing artifacts and
     artifact servers are not compatible, as such remote artifact servers need to
diff --git a/doc/bst2html.py b/doc/bst2html.py
index 2f4012695..448ab1389 100755
--- a/doc/bst2html.py
+++ b/doc/bst2html.py
@@ -29,7 +29,6 @@ import sys
 import re
 import shlex
 import subprocess
-from collections.abc import Mapping
 from contextlib import contextmanager
 from tempfile import TemporaryDirectory
 
@@ -348,7 +347,7 @@ def run_session(description, tempdir, source_cache, palette, config_file, force)
     #        tarball. This workaround lets us build docs from
     #        a source distribution tarball.
     #
-    symlinks = _yaml.node_get(desc, Mapping, 'workaround-symlinks', default_value={})
+    symlinks = _yaml.node_get(desc, dict, 'workaround-symlinks', default_value={})
     for symlink, target in _yaml.node_items(symlinks):
 
         # Resolve real path to where symlink should be
@@ -382,7 +381,7 @@ def run_session(description, tempdir, source_cache, palette, config_file, force)
     #
     commands = _yaml.node_get(desc, list, 'commands')
     for c in commands:
-        command = _yaml.node_get(desc, Mapping, 'commands', indices=[commands.index(c)])
+        command = _yaml.node_get(desc, dict, 'commands', indices=[commands.index(c)])
 
         # Get the directory where this command should be run
         directory = _yaml.node_get(command, str, 'directory')
diff --git a/src/buildstream/_context.py b/src/buildstream/_context.py
index 151ea636a..3f6e6ac3c 100644
--- a/src/buildstream/_context.py
+++ b/src/buildstream/_context.py
@@ -21,7 +21,6 @@ import os
 import shutil
 import datetime
 from collections import deque
-from collections.abc import Mapping
 from contextlib import contextmanager
 from . import utils
 from . import _cachekey
@@ -252,7 +251,7 @@ class Context():
         # Load quota configuration
         # We need to find the first existing directory in the path of our
         # cachedir - the cachedir may not have been created yet.
-        cache = _yaml.node_get(defaults, Mapping, 'cache')
+        cache = _yaml.node_get(defaults, dict, 'cache')
         _yaml.node_validate(cache, ['quota', 'pull-buildtrees', 'cache-buildtrees'])
 
         self.config_cache_quota_string = _yaml.node_get(cache, str, 'quota')
@@ -281,7 +280,7 @@ class Context():
             cache, 'cache-buildtrees', ['always', 'auto', 'never'])
 
         # Load logging config
-        logging = _yaml.node_get(defaults, Mapping, 'logging')
+        logging = _yaml.node_get(defaults, dict, 'logging')
         _yaml.node_validate(logging, [
             'key-length', 'verbose',
             'error-lines', 'message-lines',
@@ -296,7 +295,7 @@ class Context():
         self.log_message_format = _yaml.node_get(logging, str, 'message-format')
 
         # Load scheduler config
-        scheduler = _yaml.node_get(defaults, Mapping, 'scheduler')
+        scheduler = _yaml.node_get(defaults, dict, 'scheduler')
         _yaml.node_validate(scheduler, [
             'on-error', 'fetchers', 'builders',
             'pushers', 'network-retries'
@@ -406,10 +405,10 @@ class Context():
     #    project_name (str): The project name
     #
     # Returns:
-    #    (Mapping): The overrides dictionary for the specified project
+    #    (dict): The overrides dictionary for the specified project
     #
     def get_overrides(self, project_name):
-        return _yaml.node_get(self._project_overrides, Mapping, project_name, default_value={})
+        return _yaml.node_get(self._project_overrides, dict, project_name, default_value={})
 
     # get_strict():
     #
diff --git a/src/buildstream/_gitsourcebase.py b/src/buildstream/_gitsourcebase.py
index 7d07c56cb..7f02af40d 100644
--- a/src/buildstream/_gitsourcebase.py
+++ b/src/buildstream/_gitsourcebase.py
@@ -24,7 +24,6 @@
 import os
 import re
 import shutil
-from collections.abc import Mapping
 from io import StringIO
 from tempfile import TemporaryFile
 
@@ -413,9 +412,9 @@ class _GitSourceBase(Source):
         # and submodule_checkout_overrides dictionaries.
         self.submodule_overrides = {}
         self.submodule_checkout_overrides = {}
-        modules = self.node_get_member(node, Mapping, 'submodules', {})
+        modules = self.node_get_member(node, dict, 'submodules', {})
         for path, _ in self.node_items(modules):
-            submodule = self.node_get_member(modules, Mapping, path)
+            submodule = self.node_get_member(modules, dict, path)
             url = self.node_get_member(submodule, str, 'url', None)
 
             # Make sure to mark all URLs that are specified in the configuration
diff --git a/src/buildstream/_loader/loader.py b/src/buildstream/_loader/loader.py
index e279501ff..752883d96 100644
--- a/src/buildstream/_loader/loader.py
+++ b/src/buildstream/_loader/loader.py
@@ -19,7 +19,6 @@
 
 import os
 from functools import cmp_to_key
-from collections.abc import Mapping
 
 from .._exceptions import LoadError, LoadErrorReason
 from .. import Consistency
@@ -475,7 +474,7 @@ class Loader():
         # Safe loop calling into _yaml.node_get() for each element ensures
         # we have good error reporting
         for i in range(len(sources)):
-            source = _yaml.node_get(node, Mapping, Symbol.SOURCES, indices=[i])
+            source = _yaml.node_get(node, dict, Symbol.SOURCES, indices=[i])
             kind = _yaml.node_get(source, str, Symbol.KIND)
             _yaml.node_del(source, Symbol.KIND)
 
@@ -490,12 +489,12 @@ class Loader():
 
         meta_element = MetaElement(self.project, element.name, element_kind,
                                    elt_provenance, meta_sources,
-                                   _yaml.node_get(node, Mapping, Symbol.CONFIG, default_value={}),
-                                   _yaml.node_get(node, Mapping, Symbol.VARIABLES, default_value={}),
-                                   _yaml.node_get(node, Mapping, Symbol.ENVIRONMENT, default_value={}),
+                                   _yaml.node_get(node, dict, Symbol.CONFIG, default_value={}),
+                                   _yaml.node_get(node, dict, Symbol.VARIABLES, default_value={}),
+                                   _yaml.node_get(node, dict, Symbol.ENVIRONMENT, default_value={}),
                                    _yaml.node_get(node, list, Symbol.ENV_NOCACHE, default_value=[]),
-                                   _yaml.node_get(node, Mapping, Symbol.PUBLIC, default_value={}),
-                                   _yaml.node_get(node, Mapping, Symbol.SANDBOX, default_value={}),
+                                   _yaml.node_get(node, dict, Symbol.PUBLIC, default_value={}),
+                                   _yaml.node_get(node, dict, Symbol.SANDBOX, default_value={}),
                                    element_kind == 'junction')
 
         # Cache it now, make sure it's already there before recursing
diff --git a/src/buildstream/_project.py b/src/buildstream/_project.py
index c40321c66..1fdc84acb 100644
--- a/src/buildstream/_project.py
+++ b/src/buildstream/_project.py
@@ -21,7 +21,6 @@
 import os
 import sys
 from collections import OrderedDict
-from collections.abc import Mapping
 from pathlib import Path
 from pluginbase import PluginBase
 from . import utils
@@ -606,7 +605,7 @@ class Project():
         self.config.options = OptionPool(self.element_path)
         self.first_pass_config.options = OptionPool(self.element_path)
 
-        defaults = _yaml.node_get(pre_config_node, Mapping, 'defaults')
+        defaults = _yaml.node_get(pre_config_node, dict, 'defaults')
         _yaml.node_validate(defaults, ['targets'])
         self._default_targets = _yaml.node_get(defaults, list, "targets")
 
@@ -683,14 +682,14 @@ class Project():
             self.remote_execution_specs = self._context.remote_execution_specs
 
         # Load sandbox environment variables
-        self.base_environment = _yaml.node_get(config, Mapping, 'environment')
+        self.base_environment = _yaml.node_get(config, dict, 'environment')
         self.base_env_nocache = _yaml.node_get(config, list, 'environment-nocache')
 
         # Load sandbox configuration
-        self._sandbox = _yaml.node_get(config, Mapping, 'sandbox')
+        self._sandbox = _yaml.node_get(config, dict, 'sandbox')
 
         # Load project split rules
-        self._splits = _yaml.node_get(config, Mapping, 'split-rules')
+        self._splits = _yaml.node_get(config, dict, 'split-rules')
 
         # Support backwards compatibility for fail-on-overlap
         fail_on_overlap = _yaml.node_get(config, bool, 'fail-on-overlap', default_value=None)
@@ -714,12 +713,12 @@ class Project():
             self.refs.load(self.options)
 
         # Parse shell options
-        shell_options = _yaml.node_get(config, Mapping, 'shell')
+        shell_options = _yaml.node_get(config, dict, 'shell')
         _yaml.node_validate(shell_options, ['command', 'environment', 'host-files'])
         self._shell_command = _yaml.node_get(shell_options, list, 'command')
 
         # Perform environment expansion right away
-        shell_environment = _yaml.node_get(shell_options, Mapping, 'environment', default_value={})
+        shell_environment = _yaml.node_get(shell_options, dict, 'environment', default_value={})
         for key in _yaml.node_keys(shell_environment):
             value = _yaml.node_get(shell_environment, str, key)
             self._shell_environment[key] = os.path.expandvars(value)
@@ -732,7 +731,7 @@ class Project():
             else:
                 # Some validation
                 index = host_files.index(host_file)
-                host_file_desc = _yaml.node_get(shell_options, Mapping, 'host-files', indices=[index])
+                host_file_desc = _yaml.node_get(shell_options, dict, 'host-files', indices=[index])
                 _yaml.node_validate(host_file_desc, ['path', 'host_path', 'optional'])
 
                 # Parse the host mount
@@ -759,8 +758,8 @@ class Project():
         # Element and Source  type configurations will be composited later onto
         # element/source types, so we delete it from here and run our final
         # assertion after.
-        output.element_overrides = _yaml.node_get(config, Mapping, 'elements', default_value={})
-        output.source_overrides = _yaml.node_get(config, Mapping, 'sources', default_value={})
+        output.element_overrides = _yaml.node_get(config, dict, 'elements', default_value={})
+        output.source_overrides = _yaml.node_get(config, dict, 'sources', default_value={})
         _yaml.node_del(config, 'elements', safe=True)
         _yaml.node_del(config, 'sources', safe=True)
         _yaml.node_final_assertions(config)
@@ -768,7 +767,7 @@ class Project():
         self._load_plugin_factories(config, output)
 
         # Load project options
-        options_node = _yaml.node_get(config, Mapping, 'options', default_value={})
+        options_node = _yaml.node_get(config, dict, 'options', default_value={})
         output.options.load(options_node)
         if self.junction:
             # load before user configuration
@@ -776,7 +775,7 @@ class Project():
 
         # Collect option values specified in the user configuration
         overrides = self._context.get_overrides(self.name)
-        override_options = _yaml.node_get(overrides, Mapping, 'options', default_value={})
+        override_options = _yaml.node_get(overrides, dict, 'options', default_value={})
         output.options.load_yaml_values(override_options)
         if self._cli_options:
             output.options.load_cli_values(self._cli_options, ignore_unknown=ignore_unknown)
@@ -795,7 +794,7 @@ class Project():
         output.options.process_node(output.source_overrides)
 
         # Load base variables
-        output.base_variables = _yaml.node_get(config, Mapping, 'variables')
+        output.base_variables = _yaml.node_get(config, dict, 'variables')
 
         # Add the project name as a default variable
         _yaml.node_set(output.base_variables, 'project-name', self.name)
@@ -823,7 +822,7 @@ class Project():
             _yaml.node_validate(mirror, allowed_mirror_fields)
             mirror_name = _yaml.node_get(mirror, str, 'name')
             alias_mappings = {}
-            for alias_mapping, uris in _yaml.node_items(_yaml.node_get(mirror, Mapping, 'aliases')):
+            for alias_mapping, uris in _yaml.node_items(_yaml.node_get(mirror, dict, 'aliases')):
                 assert isinstance(uris, list)
                 alias_mappings[alias_mapping] = list(uris)
             output.mirrors[mirror_name] = alias_mappings
@@ -831,7 +830,7 @@ class Project():
                 output.default_mirror = mirror_name
 
         # Source url aliases
-        output._aliases = _yaml.node_get(config, Mapping, 'aliases', default_value={})
+        output._aliases = _yaml.node_get(config, dict, 'aliases', default_value={})
 
     # _find_project_dir()
     #
@@ -894,7 +893,7 @@ class Project():
                     .format(origin_value))
 
             # Store source versions for checking later
-            source_versions = _yaml.node_get(origin, Mapping, 'sources', default_value={})
+            source_versions = _yaml.node_get(origin, dict, 'sources', default_value={})
             for key in _yaml.node_keys(source_versions):
                 if key in source_format_versions:
                     raise LoadError(
@@ -903,7 +902,7 @@ class Project():
                 source_format_versions[key] = _yaml.node_get(source_versions, int, key)
 
             # Store element versions for checking later
-            element_versions = _yaml.node_get(origin, Mapping, 'elements', default_value={})
+            element_versions = _yaml.node_get(origin, dict, 'elements', default_value={})
             for key in _yaml.node_keys(element_versions):
                 if key in element_format_versions:
                     raise LoadError(
@@ -947,7 +946,7 @@ class Project():
         node_keys = [key for key in _yaml.node_keys(origin)]
         if plugin_group in node_keys:
             origin_node = _yaml.node_copy(origin)
-            plugins = _yaml.node_get(origin, Mapping, plugin_group, default_value={})
+            plugins = _yaml.node_get(origin, dict, plugin_group, default_value={})
             _yaml.node_set(origin_node, 'plugins', [k for k in _yaml.node_keys(plugins)])
             for group in expected_groups:
                 if group in origin_node:
diff --git a/src/buildstream/_yaml.pyx b/src/buildstream/_yaml.pyx
index 50f0c64a9..b33858e86 100644
--- a/src/buildstream/_yaml.pyx
+++ b/src/buildstream/_yaml.pyx
@@ -547,12 +547,12 @@ cpdef object node_get(Node node, object expected_type, str key, list indices=Non
     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.value, expected_type)):
+    if (expected_type is not None) and (type(value.value) is not 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.value, str)):
+            if expected_type == bool and type(value.value) is 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.value in ('True', 'true'):
diff --git a/src/buildstream/element.py b/src/buildstream/element.py
index 8e006ea6b..909a0e851 100644
--- a/src/buildstream/element.py
+++ b/src/buildstream/element.py
@@ -77,7 +77,6 @@ import re
 import stat
 import copy
 from collections import OrderedDict
-from collections.abc import Mapping
 import contextlib
 from contextlib import contextmanager
 from functools import partial
@@ -886,7 +885,7 @@ class Element(Plugin):
         if self.__dynamic_public is None:
             self.__load_public_data()
 
-        data = _yaml.node_get(self.__dynamic_public, Mapping, domain, default_value=None)
+        data = _yaml.node_get(self.__dynamic_public, dict, domain, default_value=None)
         if data is not None:
             data = _yaml.node_copy(data)
 
@@ -2434,9 +2433,9 @@ class Element(Plugin):
     @classmethod
     def __compose_default_splits(cls, project, defaults, is_junction):
 
-        element_public = _yaml.node_get(defaults, Mapping, 'public', default_value={})
-        element_bst = _yaml.node_get(element_public, Mapping, 'bst', default_value={})
-        element_splits = _yaml.node_get(element_bst, Mapping, 'split-rules', default_value={})
+        element_public = _yaml.node_get(defaults, dict, 'public', default_value={})
+        element_bst = _yaml.node_get(element_public, dict, 'bst', default_value={})
+        element_splits = _yaml.node_get(element_bst, dict, 'split-rules', default_value={})
 
         if is_junction:
             splits = _yaml.node_copy(element_splits)
@@ -2476,7 +2475,7 @@ class Element(Plugin):
             else:
                 elements = project.element_overrides
 
-            overrides = _yaml.node_get(elements, Mapping, kind, default_value=None)
+            overrides = _yaml.node_get(elements, dict, kind, default_value=None)
             if overrides:
                 _yaml.composite(defaults, overrides)
 
@@ -2488,7 +2487,7 @@ class Element(Plugin):
     #
     @classmethod
     def __extract_environment(cls, project, meta):
-        default_env = _yaml.node_get(cls.__defaults, Mapping, 'environment', default_value={})
+        default_env = _yaml.node_get(cls.__defaults, dict, 'environment', default_value={})
 
         if meta.is_junction:
             environment = _yaml.new_empty_node()
@@ -2534,7 +2533,7 @@ class Element(Plugin):
     #
     @classmethod
     def __extract_variables(cls, project, meta):
-        default_vars = _yaml.node_get(cls.__defaults, Mapping, 'variables',
+        default_vars = _yaml.node_get(cls.__defaults, dict, 'variables',
                                       default_value={})
 
         if meta.is_junction:
@@ -2562,7 +2561,7 @@ class Element(Plugin):
     def __extract_config(cls, meta):
 
         # The default config is already composited with the project overrides
-        config = _yaml.node_get(cls.__defaults, Mapping, 'config', default_value={})
+        config = _yaml.node_get(cls.__defaults, dict, 'config', default_value={})
         config = _yaml.node_copy(config)
 
         _yaml.composite(config, meta.config)
@@ -2588,7 +2587,7 @@ class Element(Plugin):
         host_os = platform.get_host_os()
 
         # The default config is already composited with the project overrides
-        sandbox_defaults = _yaml.node_get(cls.__defaults, Mapping, 'sandbox', default_value={})
+        sandbox_defaults = _yaml.node_get(cls.__defaults, dict, 'sandbox', default_value={})
         sandbox_defaults = _yaml.node_copy(sandbox_defaults)
 
         _yaml.composite(sandbox_config, sandbox_defaults)
@@ -2615,15 +2614,15 @@ class Element(Plugin):
     #
     @classmethod
     def __extract_public(cls, meta):
-        base_public = _yaml.node_get(cls.__defaults, Mapping, 'public', default_value={})
+        base_public = _yaml.node_get(cls.__defaults, dict, 'public', default_value={})
         base_public = _yaml.node_copy(base_public)
 
-        base_bst = _yaml.node_get(base_public, Mapping, 'bst', default_value={})
-        base_splits = _yaml.node_get(base_bst, Mapping, 'split-rules', default_value={})
+        base_bst = _yaml.node_get(base_public, dict, 'bst', default_value={})
+        base_splits = _yaml.node_get(base_bst, dict, 'split-rules', default_value={})
 
         element_public = _yaml.node_copy(meta.public)
-        element_bst = _yaml.node_get(element_public, Mapping, 'bst', default_value={})
-        element_splits = _yaml.node_get(element_bst, Mapping, 'split-rules', default_value={})
+        element_bst = _yaml.node_get(element_public, dict, 'bst', default_value={})
+        element_splits = _yaml.node_get(element_bst, dict, 'split-rules', default_value={})
 
         # Allow elements to extend the default splits defined in their project or
         # element specific defaults
@@ -2638,8 +2637,8 @@ class Element(Plugin):
 
     # Expand the splits in the public data using the Variables in the element
     def __expand_splits(self, element_public):
-        element_bst = _yaml.node_get(element_public, Mapping, 'bst', default_value={})
-        element_splits = _yaml.node_get(element_bst, Mapping, 'split-rules', default_value={})
+        element_bst = _yaml.node_get(element_public, dict, 'bst', default_value={})
+        element_splits = _yaml.node_get(element_bst, dict, 'split-rules', default_value={})
 
         # Resolve any variables in the public split rules directly
         for domain, splits in self.node_items(element_splits):
diff --git a/src/buildstream/plugins/elements/junction.py b/src/buildstream/plugins/elements/junction.py
index 15ef115d9..4222de360 100644
--- a/src/buildstream/plugins/elements/junction.py
+++ b/src/buildstream/plugins/elements/junction.py
@@ -162,7 +162,6 @@ Note that when targeting another junction, the names of the junction element
 must not be the same as the name of the target.
 """
 
-from collections.abc import Mapping
 from buildstream import Element, ElementError
 from buildstream._pipeline import PipelineError
 
@@ -177,7 +176,7 @@ class JunctionElement(Element):
 
     def configure(self, node):
         self.path = self.node_get_member(node, str, 'path', default='')
-        self.options = self.node_get_member(node, Mapping, 'options', default={})
+        self.options = self.node_get_member(node, dict, 'options', default={})
         self.target = self.node_get_member(node, str, 'target', default=None)
         self.target_element = None
         self.target_junction = None
diff --git a/src/buildstream/source.py b/src/buildstream/source.py
index f6cefb386..9fc9cf17d 100644
--- a/src/buildstream/source.py
+++ b/src/buildstream/source.py
@@ -162,7 +162,6 @@ Class Reference
 """
 
 import os
-from collections.abc import Mapping
 from contextlib import contextmanager
 
 from . import _yaml, utils
@@ -1280,7 +1279,7 @@ class Source(Plugin):
                 sources = project.first_pass_config.source_overrides
             else:
                 sources = project.source_overrides
-            cls.__defaults = _yaml.node_get(sources, Mapping, meta.kind, default_value={})
+            cls.__defaults = _yaml.node_get(sources, dict, meta.kind, default_value={})
             cls.__defaults_set = True
 
     # This will resolve the final configuration to be handed
@@ -1288,7 +1287,7 @@ class Source(Plugin):
     #
     @classmethod
     def __extract_config(cls, meta):
-        config = _yaml.node_get(cls.__defaults, Mapping, 'config', default_value={})
+        config = _yaml.node_get(cls.__defaults, dict, 'config', default_value={})
         config = _yaml.node_copy(config)
 
         _yaml.composite(config, meta.config)
diff --git a/tests/internals/yaml.py b/tests/internals/yaml.py
index 6b26fdfaf..cd3bdc535 100644
--- a/tests/internals/yaml.py
+++ b/tests/internals/yaml.py
@@ -1,4 +1,3 @@
-from collections.abc import Mapping
 import os
 from io import StringIO
 
@@ -108,12 +107,12 @@ def test_node_get(datafiles):
     assert isinstance(children, list)
     assert len(children) == 7
 
-    child = _yaml.node_get(base, Mapping, 'children', indices=[6])
+    child = _yaml.node_get(base, dict, 'children', indices=[6])
     assert_provenance(filename, 20, 8, child, 'mood')
 
-    extra = _yaml.node_get(base, Mapping, 'extra')
+    extra = _yaml.node_get(base, dict, 'extra')
     with pytest.raises(LoadError) as exc:
-        _yaml.node_get(extra, Mapping, 'old')
+        _yaml.node_get(extra, dict, 'old')
 
     assert exc.value.reason == LoadErrorReason.INVALID_DATA
 
@@ -189,8 +188,8 @@ def test_composite_preserve_originals(datafiles):
     base_copy = _yaml.node_copy(base)
     _yaml.composite_dict(base_copy, overlay)
 
-    copy_extra = _yaml.node_get(base_copy, Mapping, 'extra')
-    orig_extra = _yaml.node_get(base, Mapping, 'extra')
+    copy_extra = _yaml.node_get(base_copy, dict, 'extra')
+    orig_extra = _yaml.node_get(base, dict, 'extra')
 
     # Test that the node copy has the overridden value...
     assert _yaml.node_get(copy_extra, str, 'old') == 'override'
@@ -474,7 +473,7 @@ def test_roundtrip_dump(datafiles, fromdisk):
         for v in node.values():
             if isinstance(v, list):
                 walk_list(v)
-            elif isinstance(v, Mapping):
+            elif isinstance(v, dict):
                 walk_node(v)
             else:
                 assert isinstance(v, str)
@@ -483,7 +482,7 @@ def test_roundtrip_dump(datafiles, fromdisk):
         for v in l:
             if isinstance(v, list):
                 walk_list(v)
-            elif isinstance(v, Mapping):
+            elif isinstance(v, dict):
                 walk_node(v)
             else:
                 assert isinstance(v, str)