add unit() function

tests/test_formula_evaluate.py

@@ -225,6 +225,29 @@ def evaluate_expr(source: str, columns: dict[str, Col]) -> object:
         columns={"ra": Col("00 02 08.4")},
         error=True,
     ),
+    EvalCase(
+        name="unit_from_string",
+        expression='unit("km")',
+        columns={},
+        result_val=1.0,
+        result_unit=u.km,
+    ),
+    EvalCase(
+        name="unit_multiplied",
+        expression='col("float_col") * unit("Mpc")',
+        columns=_COLUMNS,
+        result_val=1.5,
+        result_unit=u.Mpc,
+    ),
+    EvalCase(
+        name="unit_composite",
+        expression='col("float_col") * unit("km/s")',
+        columns=_COLUMNS,
+        result_val=1.5,
+        result_unit=u.km / u.s,
+    ),
+    EvalCase(name="error_unknown_unit", expression='unit("not_a_unit")', columns={}, error=True),
+    EvalCase(name="error_unit_non_string", expression="unit(1)", columns={}, error=True),
 ]
 
 

tests/test_formula_parse.py

@@ -7,6 +7,7 @@
     ('col("weird name")', {"weird name"}),
     ('sin(col("pa")) + pi', {"pa"}),
     ('to_deg(col("RAJ2000"))', {"RAJ2000"}),
+    ('col("dist") * unit("Mpc")', {"dist"}),
     ('3 * 10 ** col("logd25") * col("e_logd25") * arcsec', {"logd25", "e_logd25"}),
     ('"M " + col("id")', {"id"}),
     ("1 + 2", set()),

tests/test_formula_tokens.py

@@ -4,7 +4,7 @@
 
 def test_expression_tokens_include_language_names() -> None:
     labels = {token["label"] for token in expression_tokens()}
-    assert labels >= {"col", "sin", "cos", "str", "to_deg", "pi", "deg", "arcsec", "mag"}
+    assert labels >= {"col", "sin", "cos", "str", "to_deg", "unit", "pi", "deg", "arcsec", "mag"}
 
 
 def test_designation_form_marks_expression_widget() -> None:

tests/test_formula_validate.py

@@ -6,6 +6,7 @@
 def test_validate_expression_accepts_valid() -> None:
     assert validate_expression('to_deg(col("RAJ2000"))') == []
     assert validate_expression("sin(pi) + 1.5 * deg") == []
+    assert validate_expression('col("dist") * unit("Mpc")') == []
     assert validate_expression("") == []
 
 

uploader/app/lib/formula/namespace.py

@@ -101,13 +101,29 @@ def _to_deg(value: object) -> u.Quantity:
     raise TypeError(f"to_deg() expected angle or coordinate string, got {type(value).__name__}")
 
 
+def _unit(name: object) -> u.Quantity:
+    if not isinstance(name, str):
+        raise TypeError(f"unit() expected a unit name string, got {type(name).__name__}")
+    return 1 * u.Unit(name)
+
+
 COL_FUNCTION = FunctionDef("col", "Rawdata column", placeholder='"${1:name}"')
 
 FUNCTIONS: tuple[FunctionDef, ...] = (
     FunctionDef("sin", "Sine (argument must be an angle)", np.sin),
     FunctionDef("cos", "Cosine (argument must be an angle)", np.cos),
     FunctionDef("str", "Convert to text", _formula_str),
-    FunctionDef("to_deg", "Convert to degrees; parses coordinate strings or angle quantities", _to_deg),
+    FunctionDef(
+        "to_deg",
+        'Convert to degrees; e.g. "00 02 08.4" (hourangle), "+16 35 13" (deg), "00h02m08.4s"',
+        _to_deg,
+    ),
+    FunctionDef(
+        "unit",
+        'Astropy unit from a name string; e.g. "Mpc", "km/s", "Jy"',
+        _unit,
+        placeholder='"${1:name}"',
+    ),
 )
 
 
@@ -182,5 +198,4 @@ def expression_syntax_help() -> str:
     - `180 * deg`
     - `"G"` - fills the column with a text "G"
 - Copy another column: `col("ra")`
-- Sexagesimal coordinates: `to_deg(col("RAJ2000"))`
 - Mathematical expression: `3 * 10 ** col("logd25") * arcsec`"""