Better support for realizing scalar YAML values (ufs-community#512)

src/uwtools/config/formats/yaml.py

@@ -1,17 +1,13 @@
+from collections import OrderedDict
 from pathlib import Path
 from types import SimpleNamespace as ns
 from typing import Optional
 
 import yaml
+from f90nml import Namelist  # type: ignore
 
 from uwtools.config.formats.base import Config
-from uwtools.config.support import (
-    INCLUDE_TAG,
-    UWYAMLConvert,
-    UWYAMLRemove,
-    add_yaml_representers,
-    log_and_error,
-)
+from uwtools.config.support import INCLUDE_TAG, UWYAMLConvert, UWYAMLRemove, from_od, log_and_error
 from uwtools.exceptions import UWConfigError
 from uwtools.strings import FORMAT
 from uwtools.utils.file import readable, writable
@@ -52,7 +48,7 @@ def __repr__(self) -> str:
         """
         The string representation of a YAMLConfig object.
         """
-        add_yaml_representers()
+        self._add_yaml_representers()
         return yaml.dump(self.data, default_flow_style=False).strip()
 
     # Private methods
@@ -120,15 +116,15 @@ def dump(self, path: Optional[Path] = None) -> None:
         """
         self.dump_dict(self.data, path)
 
-    @staticmethod
-    def dump_dict(cfg: dict, path: Optional[Path] = None) -> None:
+    @classmethod
+    def dump_dict(cls, cfg: dict, path: Optional[Path] = None) -> None:
         """
         Dumps a provided config dictionary in YAML format.
 
         :param cfg: The in-memory config object to dump.
         :param path: Path to dump config to.
         """
-        add_yaml_representers()
+        cls._add_yaml_representers()
         with writable(path) as f:
             yaml.dump(cfg, f, sort_keys=False)
 
@@ -145,3 +141,52 @@ def get_format() -> str:
         Returns the config's format name.
         """
         return FORMAT.yaml
+
+    # Private methods
+
+    @classmethod
+    def _add_yaml_representers(cls) -> None:
+        """
+        Add representers to the YAML dumper for custom types.
+        """
+        yaml.add_representer(UWYAMLConvert, UWYAMLConvert.represent)
+        yaml.add_representer(Namelist, cls._represent_namelist)
+        yaml.add_representer(OrderedDict, cls._represent_ordereddict)
+
+    @classmethod
+    def _represent_namelist(cls, dumper: yaml.Dumper, data: Namelist) -> yaml.nodes.MappingNode:
+        """
+        Convert an f90nml Namelist to an OrderedDict, then represent as a YAML mapping.
+
+        :param dumper: The YAML dumper.
+        :param data: The f90nml Namelist to serialize.
+        """
+        namelist_dict = data.todict()
+        return dumper.represent_mapping("tag:yaml.org,2002:map", namelist_dict)
+
+    @classmethod
+    def _represent_ordereddict(
+        cls, dumper: yaml.Dumper, data: OrderedDict
+    ) -> yaml.nodes.MappingNode:
+        """
+        Recursrively convert an OrderedDict to a dict, then represent as a YAML mapping.
+
+        :param dumper: The YAML dumper.
+        :param data: The OrderedDict to serialize.
+        """
+
+        return dumper.represent_mapping("tag:yaml.org,2002:map", from_od(data))
+
+
+def _write_plain_open_ended(self, *args, **kwargs) -> None:
+    """
+    Write YAML without ...
+
+    end-of-stream marker.
+    """
+    self.write_plain_base(*args, **kwargs)
+    self.open_ended = False
+
+
+setattr(yaml.emitter.Emitter, "write_plain_base", yaml.emitter.Emitter.write_plain)
+setattr(yaml.emitter.Emitter, "write_plain", _write_plain_open_ended)

src/uwtools/config/support.py

@@ -5,7 +5,6 @@
 from typing import Dict, Type, Union
 
 import yaml
-from f90nml import Namelist  # type: ignore
 
 from uwtools.exceptions import UWConfigError
 from uwtools.logging import log
@@ -17,15 +16,6 @@
 # Public functions
 
 
-def add_yaml_representers() -> None:
-    """
-    Add representers to the YAML dumper for custom types.
-    """
-    yaml.add_representer(UWYAMLConvert, UWYAMLConvert.represent)
-    yaml.add_representer(Namelist, _represent_namelist)
-    yaml.add_representer(OrderedDict, _represent_ordereddict)
-
-
 def depth(d: dict) -> int:
     """
     The depth of a dictionary.
@@ -76,31 +66,6 @@ def log_and_error(msg: str) -> Exception:
     return UWConfigError(msg)
 
 
-# Private functions
-
-
-def _represent_namelist(dumper: yaml.Dumper, data: Namelist) -> yaml.nodes.MappingNode:
-    """
-    Convert an f90nml Namelist to an OrderedDict, then represent as a YAML mapping.
-
-    :param dumper: The YAML dumper.
-    :param data: The f90nml Namelist to serialize.
-    """
-    namelist_dict = data.todict()
-    return dumper.represent_mapping("tag:yaml.org,2002:map", namelist_dict)
-
-
-def _represent_ordereddict(dumper: yaml.Dumper, data: OrderedDict) -> yaml.nodes.MappingNode:
-    """
-    Recursrively convert an OrderedDict to a dict, then represent as a YAML mapping.
-
-    :param dumper: The YAML dumper.
-    :param data: The OrderedDict to serialize.
-    """
-
-    return dumper.represent_mapping("tag:yaml.org,2002:map", from_od(data))
-
-
 class UWYAMLTag:
     """
     A base class for custom UW YAML tags.

src/uwtools/tests/config/formats/test_yaml.py

@@ -1,4 +1,4 @@
-# pylint: disable=missing-function-docstring
+# pylint: disable=missing-function-docstring,protected-access
 """
 Tests for uwtools.config.formats.yaml module.
 """
@@ -7,10 +7,12 @@
 import filecmp
 import logging
 import sys
+from collections import OrderedDict
 from io import StringIO
 from textwrap import dedent
 from unittest.mock import patch
 
+import f90nml  # type: ignore
 import yaml
 from pytest import raises
 
@@ -175,3 +177,25 @@ def test_unexpected_error(tmp_path):
         with raises(UWConfigError) as e:
             YAMLConfig(config=cfgfile)
         assert msg in str(e.value)
+
+
+def test__add_yaml_representers():
+    YAMLConfig._add_yaml_representers()
+    representers = yaml.Dumper.yaml_representers
+    assert support.UWYAMLConvert in representers
+    assert OrderedDict in representers
+    assert f90nml.Namelist in representers
+
+
+def test__represent_namelist():
+    YAMLConfig._add_yaml_representers()
+    namelist = f90nml.reads("&namelist\n key = value\n/\n")
+    expected = "{namelist: {key: value}}"
+    assert yaml.dump(namelist, default_flow_style=True).strip() == expected
+
+
+def test__represent_ordereddict():
+    YAMLConfig._add_yaml_representers()
+    ordereddict_values = OrderedDict([("example", OrderedDict([("key", "value")]))])
+    expected = "{example: {key: value}}"
+    assert yaml.dump(ordereddict_values, default_flow_style=True).strip() == expected

src/uwtools/tests/config/test_support.py

@@ -6,10 +6,8 @@
 import logging
 from collections import OrderedDict
 
-import f90nml  # type: ignore
 import pytest
 import yaml
-from f90nml import Namelist
 from pytest import fixture, raises
 
 from uwtools.config import support
@@ -24,14 +22,6 @@
 from uwtools.utils.file import FORMAT
 
 
-def test_add_yaml_representers():
-    support.add_yaml_representers()
-    representers = yaml.Dumper.yaml_representers
-    assert support.UWYAMLConvert in representers
-    assert OrderedDict in representers
-    assert Namelist in representers
-
-
 @pytest.mark.parametrize(
     "d,n", [({1: 88}, 1), ({1: {2: 88}}, 2), ({1: {2: {3: 88}}}, 3), ({1: {}}, 2)]
 )
@@ -73,20 +63,6 @@ def test_log_and_error(caplog):
     assert logged(caplog, msg)
 
 
-def test_represent_namelist():
-    support.add_yaml_representers()
-    namelist = f90nml.reads("&namelist\n key = value\n/\n")
-    assert yaml.dump(namelist, default_flow_style=True).strip() == "{namelist: {key: value}}"
-
-
-def test_represent_ordereddict():
-    support.add_yaml_representers()
-    ordereddict_values = OrderedDict([("example", OrderedDict([("key", "value")]))])
-    assert (
-        yaml.dump(ordereddict_values, default_flow_style=True).strip() == "{example: {key: value}}"
-    )
-
-
 class Test_UWYAMLConvert:
     """
     Tests for class uwtools.config.support.UWYAMLConvert.

src/uwtools/tests/config/test_tools.py

@@ -347,6 +347,16 @@ def test_realize_config_remove_yaml_to_yaml_subtree(tmp_path):
     )
 
 
+def test_realize_config_scalar_value(capsys):
+    stdinproxy.cache_clear()
+    tools.realize_config(
+        input_config=YAMLConfig(config={"foo": {"bar": "baz"}}),
+        output_format="yaml",
+        key_path=["foo", "bar"],
+    )
+    assert capsys.readouterr().out.strip() == "baz"
+
+
 def test_realize_config_simple_ini(tmp_path):
     """
     Test that providing an INI file with necessary settings will create an INI config file.