Correct Lookup[]'s attributes.

Add more robustness to test case that assumes an uninitialized variable.

Author: rocky

mathics/builtin/list/associations.py

@@ -10,7 +10,7 @@
 
 from mathics.builtin.box.layout import RowBox
 from mathics.core.atoms import Integer
-from mathics.core.attributes import A_HOLD_ALL_COMPLETE, A_PROTECTED
+from mathics.core.attributes import A_HOLD_ALL_COMPLETE, A_PROTECTED, A_READ_PROTECTED
 from mathics.core.builtin import Builtin, Test
 from mathics.core.convert.expression import to_mathics_list
 from mathics.core.evaluation import Evaluation
@@ -279,7 +279,7 @@ class Lookup(Builtin):
 
     """
 
-    attributes = A_HOLD_ALL_COMPLETE | A_PROTECTED
+    attributes = A_PROTECTED | A_READ_PROTECTED
 
     messages = {
         "invrl": "The argument `1` is not a valid Association or a list of rules.",

mathics/eval/list/associations.py

@@ -6,6 +6,7 @@
 
 def eval_Lookup(assoc, key, default, evaluation: Evaluation):
     """Evaluation method for Lookup."""
+
     if assoc.has_form("Association", None):
         # Search through association elements (rules)
         for element in assoc.elements:

test/builtin/list/test_association.py

@@ -263,3 +263,24 @@ def test_map_over_associations(
         failure_message=assert_message,
         expected_messages=expected_messages,
     )
+
+
+@pytest.mark.parametrize(
+    ("str_expr", "expected_messages", "str_expected", "assert_message"),
+    [
+        (
+            'a=Association[{"F":>1,"G":>2}]; Lookup[a, "H"]',
+            None,
+            "Missing[KeyAbsent, H]",
+            "Lookup test on an association variable where the key is not found.",
+        ),
+        ("ClearAll[a];", None, "Null", None),
+    ],
+)
+def test_lookup(str_expr, expected_messages, str_expected, assert_message):
+    check_evaluation(
+        str_expr,
+        str_expected,
+        failure_message=assert_message,
+        expected_messages=expected_messages,
+    )

test/builtin/list/test_eol.py

@@ -10,6 +10,7 @@
 @pytest.mark.parametrize(
     ("str_expr", "expected_messages", "str_expected", "assert_message"),
     [
+        ("ClearAll[a];", None, "Null", None),
         (
             "Append[a, b]",
             ("Nonatomic expression expected at position 1 in Append[a, b].",),