UW-269 Extend set_config.py tool to "export" variables

src/uwtools/config.py

@@ -21,6 +21,7 @@
 import yaml
 
 from uwtools import exceptions, logger
+from uwtools.exceptions import UWConfigError
 from uwtools.j2template import J2Template
 from uwtools.logger import Logger
 from uwtools.utils import cli_helpers
@@ -752,3 +753,17 @@ def create_config_obj(
                     raise ValueError(err_msg)
                 # Dump to file:
                 dump_method(path=outfile, cfg=config_obj)
+
+
+def export_variables(config_dict: dict, section_path: list, log: Logger) -> None:
+    """
+    Allows users to export sections of the config file as environment variables.
+    """
+    for key in section_path:
+        config_dict = config_dict[key]
+    for key, value in config_dict.items():
+        if type(value) not in (bool, str, int, float):
+            log.error(f"Non-scalar variable {key} was provided")
+            raise UWConfigError("Section values provided must be scalar values")
+    for key, value in config_dict.items():
+        print(f"{key}={value}")

src/uwtools/tests/test_config.py

@@ -22,6 +22,7 @@
 
 from uwtools import config, exceptions
 from uwtools.exceptions import UWConfigError
+from uwtools.logger import Logger
 from uwtools.tests.support import compare_files, fixture_path, line_in_lines, msg_in_caplog
 from uwtools.utils import cli_helpers
 
@@ -810,3 +811,39 @@ def test_YAMLConfig__load_unexpected_error(tmp_path):
         with raises(UWConfigError) as e:
             config.YAMLConfig(config_path=cfgfile)
         assert msg in str(e.value)
+
+
+def test_export_variables_yaml(capsys):
+    config_obj = config.YAMLConfig(fixture_path("FV3_GFS_v16.yaml"))
+    section = ["sgs_tke", "profile_type"]
+    config.export_variables(config_obj.data, section, log=Logger())
+    actual = capsys.readouterr().out
+    expected = """name=fixed
+surface_value=0.0\n"""
+    assert actual == expected
+
+
+def test_export_variables_yaml_for_nonscalar():
+    config_obj = config.YAMLConfig(fixture_path("FV3_GFS_v16.yaml"))
+    section = ["o3mr"]
+    with raises(UWConfigError):
+        config.export_variables(config_obj.data, section, log=Logger())
+
+
+def test_export_variables_ini(capsys):
+    config_obj = config.INIConfig(fixture_path("simple3.ini"))
+    section = ["dessert"]
+    config.export_variables(config_obj.data, section, log=Logger())
+    actual = capsys.readouterr().out
+    expected = """type=pie
+flavor={{flavor}}
+side=False
+servings=0\n"""
+    assert actual == expected
+
+
+def test_export_variables_ini_missing_section():
+    config_obj = config.INIConfig(fixture_path("simple3.ini"))
+    section = ["sandwich"]
+    with raises(KeyError):
+        config.export_variables(config_obj.data, section, log=Logger())