fix: force subclasses to have __slots__

Author: henryiii

src/boost_histogram/_internal/axis.py

@@ -304,6 +304,9 @@ def __init__(self, bins, start, stop, **kwargs):
             The full metadata dictionary
         """
 
+        # Inheriting an axis and forgetting to add __slots__ should be an error
+        assert not hasattr(self, "__weakref__"), "Axis subclasses must have __slots__!"
+
         with KWArgs(kwargs) as k:
             metadata = k.optional("metadata")
             transform = k.optional("transform")
@@ -411,6 +414,10 @@ def __init__(self, edges, **kwargs):
         __dict__: Optional[Dict[str, Any]] = None
             The full metadata dictionary
         """
+
+        # Inheriting an axis and forgetting to add __slots__ should be an error
+        assert not hasattr(self, "__weakref__"), "Axis subclasses must have __slots__!"
+
         with KWArgs(kwargs) as k:
             metadata = k.optional("metadata")
             __dict__ = k.optional("__dict__")
@@ -492,6 +499,10 @@ def __init__(self, start, stop, **kwargs):
         __dict__: Optional[Dict[str, Any]] = None
             The full metadata dictionary
         """
+
+        # Inheriting an axis and forgetting to add __slots__ should be an error
+        assert not hasattr(self, "__weakref__"), "Axis subclasses must have __slots__!"
+
         with KWArgs(kwargs) as k:
             metadata = k.optional("metadata")
             __dict__ = k.optional("__dict__")
@@ -575,6 +586,9 @@ def __init__(self, categories, **kwargs):
             The full metadata dictionary
         """
 
+        # Inheriting an axis and forgetting to add __slots__ should be an error
+        assert not hasattr(self, "__weakref__"), "Axis subclasses must have __slots__!"
+
         with KWArgs(kwargs) as k:
             metadata = k.optional("metadata")
             __dict__ = k.optional("__dict__")
@@ -640,6 +654,10 @@ def __init__(self, categories, **kwargs):
         __dict__: Optional[Dict[str, Any]] = None
             The full metadata dictionary
         """
+
+        # Inheriting an axis and forgetting to add __slots__ should be an error
+        assert not hasattr(self, "__weakref__"), "Axis subclasses must have __slots__!"
+
         with KWArgs(kwargs) as k:
             metadata = k.optional("metadata")
             __dict__ = k.optional("__dict__")
@@ -681,6 +699,10 @@ def __init__(self, **kwargs):
         __dict__: Optional[Dict[str, Any]] = None
             The full metadata dictionary
         """
+
+        # Inheriting an axis and forgetting to add __slots__ should be an error
+        assert not hasattr(self, "__weakref__"), "Axis subclasses must have __slots__!"
+
         with KWArgs(kwargs) as k:
             metadata = k.optional("metadata")
             __dict__ = k.optional("__dict__")

tests/test_axis.py

@@ -3,6 +3,7 @@
 from pytest import approx
 
 import boost_histogram as bh
+import boost_histogram.utils
 
 import numpy as np
 from numpy.testing import assert_array_equal, assert_allclose
@@ -82,6 +83,14 @@ def test_metadata(axis, args, opt, kwargs):
     with pytest.raises(KeyError):
         axis(*args, **kwargs, __dict__={"metadata": 2}, metadata=3)
 
+    # An assertion failure should occur if you forget to set slots!
+    @boost_histogram.utils.set_family(object())
+    class TmpAxis(axis):
+        pass
+
+    with pytest.raises(AssertionError):
+        TmpAxis(*args, **kwargs)
+
 
 # The point of this ABC is to force all the tests listed here to be
 # implemented for each axis type.

tests/test_subclassing.py

@@ -11,7 +11,7 @@ class MyHist(bh.Histogram):
 
     @bh.utils.set_family(NEW_FAMILY)
     class MyRegular(bh.axis.Regular):
-        pass
+        __slots__ = ()
 
     @bh.utils.set_family(NEW_FAMILY)
     class MyIntStorage(bh.storage.Int64):