Add VariableCodeList.units attribute and tests (#289)

nomenclature/codelist.py

@@ -18,6 +18,7 @@
     VariableRenameArgError,
     VariableRenameTargetError,
 )
+from pyam.utils import is_list_like
 
 here = Path(__file__).parent.absolute()
 
@@ -450,6 +451,24 @@ class VariableCodeList(CodeList):
     code_basis: ClassVar = VariableCode
     validation_schema: ClassVar[str] = "variable"
 
+    @property
+    def units(self):
+        """Get the list of all units"""
+        units = set()
+
+        # replace "dimensionless" variables (unit: `None`) with empty string
+        # for consistency with the yaml file format
+        def to_dimensionless(u):
+            return u or ""
+
+        for variable in self.mapping.values():
+            if is_list_like(variable.unit):
+                units.update([to_dimensionless(u) for u in variable.unit])
+            else:
+                units.add(to_dimensionless(variable.unit))
+
+        return sorted(list(units))
+
     @validator("mapping")
     def check_variable_region_aggregation_args(cls, v):
         """Check that any variable "region-aggregation" mappings are valid"""

tests/test_codelist.py

@@ -17,13 +17,13 @@
 
 def test_simple_codelist():
     """Import a simple codelist"""
-    code = VariableCodeList.from_directory(
+    codelist = VariableCodeList.from_directory(
         "variable", TEST_DATA_DIR / "simple_codelist"
     )
 
-    assert "Some Variable" in code
-    assert code["Some Variable"].unit is None  # this is a dimensionless variable
-    assert type(code["Some Variable"].bool) == bool  # this is a boolean
+    assert "Some Variable" in codelist
+    assert codelist["Some Variable"].unit is None  # this is a dimensionless variable
+    assert type(codelist["Some Variable"].bool) == bool  # this is a boolean
 
 
 def test_codelist_to_yaml():
@@ -155,12 +155,21 @@ def test_end_whitespace_fails():
         )
 
 
+def test_variable_codelist_units():
+    """Check that the units-attribute works as expected"""
+    codelist = VariableCodeList.from_directory(
+        "variable", TEST_DATA_DIR / "validation_nc" / "variable"
+    )
+    assert codelist.units == ["", "EJ/yr"]
+
+
 def test_variable_codelist_multiple_units():
     """Check that multiple units work in a VariableCodeList"""
     codelist = VariableCodeList.from_directory(
         "variable", TEST_DATA_DIR / "multiple_unit_codelist"
     )
     assert codelist["Var1"].unit == ["unit1", "unit2"]
+    assert codelist.units == ["unit1", "unit2"]
 
 
 def test_to_excel_read_excel_roundtrip(tmpdir):