revert: remove condition -> expr conversion experiment

Resolves vega#3427 (comment)

altair/vegalite/v5/api.py

@@ -984,58 +984,6 @@ def when(
     return When(condition)
 
 
-def _condition_to_expr_str(c: _SelectionType | _Conditions, /) -> str:
-    """Convert the output of `alt.condition`/`when-then-otherwise` to an expression string."""
-    return _condition_to_expr_ref(c).expr
-
-
-def _condition_to_expr_ref(c: _SelectionType | _Conditions, /) -> core.ExprRef:
-    """Convert the output of `alt.condition`/`when-then-otherwise` to an `ExprRef`.
-
-    Notes
-    -----
-    - Purely to demonstrate how the translation could occur
-    - Ideally, the logic would live elsewhere
-    """
-    if isinstance(c, core.SchemaBase):
-        c = c.to_dict()
-    if not isinstance(c, dict):
-        msg = f"Expected condition of type `dict`, but got: {type(c).__name__!r}."
-        raise TypeError(msg)
-    elif "value" in c:
-        # Had to change due to 0 returning False
-        otherwise = c.get("value")
-        if conditions := c.get("condition"):
-            if not isinstance(conditions, (dict, list)):
-                msg = f"Expected nested condition of type `dict | list`, but got: {type(conditions).__name__!r}."
-                raise TypeError(msg)
-            elif isinstance(conditions, dict):
-                condition = conditions
-            elif isinstance(conditions, list) and len(conditions) == 1:
-                condition = conditions[0]
-            else:
-                msg = (
-                    f"Condition specifies {len(conditions)!r} `when-then` clauses.\n"
-                    f"`alt.expr.if_` supports only `1`, followed by an `otherwise`.\n\n"
-                    f"{c!r}"
-                )
-                raise ValueError(msg)
-
-            if when := condition.get("test"):
-                then = condition["value"]
-                expr = _expr_core.FunctionExpression("if", (when, then, otherwise))
-                return core.ExprRef(expr.to_dict())
-            else:
-                msg = f"Missing `test` key, unable to convert to `ExprRef.\n\n{c!r}"
-                raise KeyError(msg)
-        else:
-            msg = f"Missing `condition` key, equivalent to `when`, `then` clauses.\n\n{c!r}"
-            raise KeyError(msg)
-    else:
-        msg = f"Missing `value` key, equivalent to `otherwise` clause.\n\n{c!r}"
-        raise KeyError(msg)
-
-
 # ------------------------------------------------------------------------
 # Top-Level Functions
 

tests/vegalite/v5/test_api.py

@@ -253,10 +253,9 @@ def test_chart_operations():
 
 
 def test_when() -> None:
-    from altair.vegalite.v5 import api as _alt
-
     select = alt.selection_point(name="select", on="click")
-    condition = _alt._predicate_to_condition(select, empty=False)
+    condition = alt.condition(select, alt.value(1), "two", empty=False).get("condition")
+    condition.pop("value")
     when = alt.when(select, empty=False)
     when_constraint = alt.when(Origin="Europe")
     when_constraints = alt.when(
@@ -390,8 +389,6 @@ def test_when_labels_position_based_on_condition() -> None:
     import pandas as pd
     from altair.utils.schemapi import SchemaValidationError
 
-    from altair.vegalite.v5 import api as _alt
-
     rand = np.random.RandomState(42)
     df = pd.DataFrame({"xval": range(100), "yval": rand.randn(100).cumsum()})
 
@@ -409,7 +406,11 @@ def test_when_labels_position_based_on_condition() -> None:
         .then(alt.value("red"))
         .otherwise("black", str_as_lit=True)
     )
-    param_color_py_when = alt.param(expr=_alt._condition_to_expr_str(when))
+    cond = when["condition"][0]
+    otherwise = when["value"]
+    param_color_py_when = alt.param(
+        expr=alt.expr.if_(cond["test"], cond["value"], otherwise)
+    )
     assert param_color_py_expr.expr == param_color_py_when.expr
 
     chart = (
@@ -434,7 +435,6 @@ def test_when_expressions_inside_parameters() -> None:
 
     Original [expressions-inside-parameters](https://altair-viz.github.io/user_guide/interactions.html#expressions-inside-parameters)
     """
-    from altair.vegalite.v5 import api as _alt
     import pandas as pd
 
     source = pd.DataFrame({"a": ["A", "B", "C"], "b": [28, -5, 10]})
@@ -445,8 +445,10 @@ def test_when_expressions_inside_parameters() -> None:
         .encode(y="a:N", x=alt.X("b:Q").scale(domain=[-10, 35]))
     )
     when_then_otherwise = alt.when(alt.datum.b >= 0).then(10).otherwise(-20)
+    cond = when_then_otherwise["condition"][0]
+    otherwise = when_then_otherwise["value"]
     expected = alt.expr(alt.expr.if_(alt.datum.b >= 0, 10, -20))
-    actual = _alt._condition_to_expr_ref(when_then_otherwise)
+    actual = alt.expr(alt.expr.if_(cond["test"], cond["value"], otherwise))
     assert expected == actual
 
     text_conditioned = bar.mark_text(align="left", baseline="middle", dx=actual).encode(
@@ -457,45 +459,6 @@ def test_when_expressions_inside_parameters() -> None:
     chart.to_dict()
 
 
-def test_when_convert_expr() -> None:
-    from altair.vegalite.v5 import api as _alt
-
-    when = alt.when(Color="Green").then(5).otherwise(10)
-    converted = _alt._condition_to_expr_ref(when)
-
-    assert isinstance(converted, alt.ExprRef)
-
-    with pytest.raises(TypeError, match="int"):
-        _alt._condition_to_expr_ref(9)  # type: ignore
-
-    with pytest.raises(KeyError, match="Missing `value`"):
-        _alt._condition_to_expr_ref(alt.when(Color="Green").then(5).to_dict())
-
-    with pytest.raises(KeyError, match="Missing `condition`"):
-        _alt._condition_to_expr_ref({"value": 10})
-
-    with pytest.raises(TypeError, match="'str'"):
-        _alt._condition_to_expr_ref({"value": 10, "condition": "words"})  # type: ignore
-
-    with pytest.raises(KeyError, match="Missing `test`"):
-        _alt._condition_to_expr_ref(
-            alt.when(alt.selection_point("name")).then(33).otherwise(11)
-        )
-
-    long = (
-        alt.when(Color="red")
-        .then(1)
-        .when(Color="blue")
-        .then(2)
-        .when(Color="green")
-        .then(3)
-        .otherwise(0)
-    )
-
-    with pytest.raises(ValueError, match="3"):
-        _alt._condition_to_expr_ref(long)
-
-
 def test_selection_to_dict():
     brush = alt.selection_interval()