python-graphblas · eriknw · Aug 3, 2026
diff --git a/graphblas/core/ss/config.py b/graphblas/core/ss/config.py
@@ -52,8 +52,38 @@ def __init__(self, parent=None, context=None):
                     if k not in rd:  # pragma: no branch (safety)
                         rd[k] = k
             cls._initialized = True
+        # Writes are unrestricted until __init__ finishes, and the instance
+        # attributes set by then become the allowlist for __setattr__.
+        # Subclasses that add instance attributes (such as Context) must set
+        # them before calling super().__init__().
+        object.__setattr__(self, "_initializing", True)
         self._parent = parent
         self._context = context
+        object.__setattr__(self, "_internal_attrs", frozenset(self.__dict__) - {"_initializing"})
+        object.__setattr__(self, "_initializing", False)
+
+    def __setattr__(self, key, value):
+        # An instance built without running __init__ has no allowlist yet, so stay
+        # permissive rather than raising a confusing AttributeError from the guard.
+        # Properties (such as Context._context) go through so their setters run.
+        if (
+            self.__dict__.get("_initializing", True)
+            or key in self._internal_attrs
+            or isinstance(getattr(type(self), key, None), property)
+        ):
+            object.__setattr__(self, key, value)
+            return
+        if (option := key.lower()) in self._options:
+            if option in self._read_only:
+                raise AttributeError(f"Config option {option!r} is read-only")
+            raise AttributeError(
+                f"Cannot set config option {option!r} by attribute assignment; "
+                f"this does not change the config. "
+                f"Use item assignment instead: config[{option!r}] = value"
+            )
+        raise AttributeError(
+            f"Unknown config option {key!r}; known options are {sorted(self._options)}."
+        )
 
     def __delitem__(self, key):
         raise TypeError("Configuration options can't be deleted.")

diff --git a/graphblas/core/ss/context.py b/graphblas/core/ss/context.py
@@ -33,9 +33,12 @@ class Context(BaseConfig):
     }
 
     def __init__(self, engage=True, *, stack=True, nthreads=None, chunk=None, gpu_id=None):
-        super().__init__()
+        # Instance attributes must exist before super().__init__() finishes,
+        # because BaseConfig.__setattr__ allows only the attributes set by then.
         self.gb_obj = ffi_new("GxB_Context*")
         check_status_carg(lib.GxB_Context_new(self.gb_obj), "Context", self.gb_obj[0])
+        self._prev_context = None
+        super().__init__()
         if stack:
             context = threadlocal.context
             self["nthreads"] = context["nthreads"] if nthreads is None else nthreads
@@ -49,7 +52,6 @@ def __init__(self, engage=True, *, stack=True, nthreads=None, chunk=None, gpu_id
                 self["chunk"] = chunk
             if gpu_id is not None and "gpu_id" in self._options:
                 self["gpu_id"] = gpu_id
-        self._prev_context = None
         if engage:
             self.engage()
 

diff --git a/graphblas/ss/_core.py b/graphblas/ss/_core.py
@@ -316,6 +316,13 @@ def __getitem__(self, key):
             raise KeyError(key)
         raise _error_code_lookup[info](f"Failed to get info for {key}")  # pragma: no cover (safety)
 
+    def __setattr__(self, key, value):
+        # About never sets instance attributes, so any attribute write is a
+        # mistake that would otherwise create a dead attribute shadowing reads.
+        if key.lower() in self:
+            raise AttributeError(f"About option {key.lower()!r} is read-only")
+        raise AttributeError(f"Unknown About option {key!r}; known options are {sorted(self)}.")
+
     def __iter__(self):
         return iter(
             sorted(

diff --git a/graphblas/tests/test_ss_utils.py b/graphblas/tests/test_ss_utils.py
@@ -253,6 +253,64 @@ def test_global_config_key_completions():
         about[key]
 
 
+def test_global_config_attribute_assignment_raises():
+    # Attribute assignment used to create a dead instance attribute and leave
+    # the real config unchanged; now it raises and points at item assignment.
+    config = gb.ss.config
+    before = config["nthreads"]
+    with pytest.raises(AttributeError, match="item assignment"):
+        config.nthreads = before + 1
+    assert config["nthreads"] == before
+    assert "nthreads" not in config.__dict__
+    with pytest.raises(AttributeError, match="Unknown config option 'nthread'"):
+        config.nthread = before + 1
+    # Item assignment is the supported write and still works
+    config["nthreads"] = before + 1
+    assert config["nthreads"] == before + 1
+    config["nthreads"] = before
+    assert config["nthreads"] == before
+    # Reads, iteration, and key completions are unaffected by the guard
+    assert dict(config) == {k: config[k] for k in config}
+    assert set(config._ipython_key_completions_()) == set(config._options)
+
+
+def test_object_config_attribute_assignment_raises():
+    v = Vector(int, 3)
+    with pytest.raises(AttributeError, match="item assignment"):
+        v.ss.config.sparsity_control = "bitmap"
+    assert v.ss.config["sparsity_control"] == {"auto"}
+    with pytest.raises(AttributeError, match="read-only"):
+        v.ss.config.sparsity_status = "bitmap"
+    A = Matrix(int, 2, 2)
+    with pytest.raises(AttributeError, match="item assignment"):
+        A.ss.config.format = "by_col"
+    assert A.ss.config["format"] == "by_row"
+    # Item assignment is the supported write and still works
+    v.ss.config["sparsity_control"] = "bitmap"
+    assert v.ss.config["sparsity_control"] == {"bitmap"}
+    v.ss.config["sparsity_control"] = "auto"
+    assert v.ss.config["sparsity_control"] == {"auto"}
+
+
+def test_about_attribute_assignment_raises():
+    about = gb.ss.about
+    mode = about["mode"]
+    with pytest.raises(AttributeError, match="read-only"):
+        about.mode = "junk"
+    assert about["mode"] == mode
+    assert "mode" not in about.__dict__
+    with pytest.raises(AttributeError, match="Unknown About option"):
+        about.junkattr = 1
+    assert dict(about) == {k: about[k] for k in about}
+
+
+@pytest.mark.skipif("gb.core.ss._IS_SSGB7")
+def test_context_attribute_assignment_raises():
+    context = gb.ss.Context(engage=False)
+    with pytest.raises(AttributeError, match="item assignment"):
+        context.nthreads = 4
+
+
 @pytest.mark.skipif("gb.core.ss._IS_SSGB7")
 def test_context():
     context = gb.ss.Context()