feat: copy_behaviors to make sub-classing easy (#3137)

* feat: copy_behaviors to make sub-classing easy

* pylint errors and tests

* make 'copy_behaviors' safer by making it immutable

---------

Co-authored-by: Jim Pivarski <[email protected]>
Co-authored-by: Jim Pivarski <[email protected]>

Author: Saransh-cpp

src/awkward/_util.py

@@ -6,6 +6,7 @@
 import os
 import struct
 import sys
+import typing
 from collections.abc import Collection
 
 import numpy as np  # noqa: TID251
@@ -102,3 +103,18 @@ def unique_list(items: Collection[T]) -> list[T]:
         seen.add(item)
         result.append(item)
     return result
+
+
+def copy_behaviors(existing_class: typing.Any, new_class: typing.Any, behavior: dict):
+    output = {}
+
+    oldname = existing_class.__name__
+    newname = new_class.__name__
+
+    for key, value in behavior.items():
+        if oldname in key:
+            if not isinstance(key, str) and "*" not in key:
+                new_tuple = tuple(newname if k == oldname else k for k in key)
+                output[new_tuple] = value
+
+    return output

tests/test_2433_copy_behaviors.py

@@ -0,0 +1,125 @@
+# BSD 3-Clause License; see https://github.com/scikit-hep/awkward/blob/main/LICENSE
+
+from __future__ import annotations
+
+import numpy
+import pytest
+
+import awkward as ak
+
+
+def test():
+    class SuperVector:
+        def add(self, other):
+            """Add two vectors together elementwise using `x` and `y` components"""
+            return ak.zip(
+                {"x": self.x + other.x, "y": self.y + other.y},
+                with_name="VectorTwoD",
+                behavior=self.behavior,
+            )
+
+    # first sub-class
+    @ak.mixin_class(ak.behavior)
+    class VectorTwoD(SuperVector):
+        def __eq__(self, other):
+            return ak.all(self.x == other.x) and ak.all(self.y == other.y)
+
+    v = ak.Array(
+        [
+            [{"x": 1, "y": 1.1}, {"x": 2, "y": 2.2}],
+            [],
+            [{"x": 3, "y": 3.3}],
+            [
+                {"x": 4, "y": 4.4},
+                {"x": 5, "y": 5.5},
+                {"x": 6, "y": 6.6},
+            ],
+        ],
+        with_name="VectorTwoD",
+        behavior=ak.behavior,
+    )
+    v_added = ak.Array(
+        [
+            [{"x": 2, "y": 2.2}, {"x": 4, "y": 4.4}],
+            [],
+            [{"x": 6, "y": 6.6}],
+            [
+                {"x": 8, "y": 8.8},
+                {"x": 10, "y": 11},
+                {"x": 12, "y": 13.2},
+            ],
+        ],
+        with_name="VectorTwoD",
+        behavior=ak.behavior,
+    )
+
+    # add method works but the binary operator does not
+    assert v.add(v) == v_added
+    with pytest.raises(TypeError):
+        v + v
+
+    # registering the operator makes everything work
+    ak.behavior[numpy.add, "VectorTwoD", "VectorTwoD"] = lambda v1, v2: v1.add(v2)
+    assert v + v == v_added
+
+    # second sub-class
+    @ak.mixin_class(ak.behavior)
+    class VectorTwoDAgain(VectorTwoD):
+        pass
+
+    v = ak.Array(
+        [
+            [{"x": 1, "y": 1.1}, {"x": 2, "y": 2.2}],
+            [],
+            [{"x": 3, "y": 3.3}],
+            [
+                {"x": 4, "y": 4.4},
+                {"x": 5, "y": 5.5},
+                {"x": 6, "y": 6.6},
+            ],
+        ],
+        with_name="VectorTwoDAgain",
+        behavior=ak.behavior,
+    )
+    # add method works but the binary operator does not
+    assert v.add(v) == v_added
+    with pytest.raises(TypeError):
+        v + v
+
+    # instead of registering every operator again, just copy the behaviors of
+    # another class to this class
+    ak.behavior.update(
+        ak._util.copy_behaviors(VectorTwoD, VectorTwoDAgain, ak.behavior)
+    )
+    assert v + v == v_added
+
+    # third sub-class
+    @ak.mixin_class(ak.behavior)
+    class VectorTwoDAgainAgain(VectorTwoDAgain):
+        pass
+
+    v = ak.Array(
+        [
+            [{"x": 1, "y": 1.1}, {"x": 2, "y": 2.2}],
+            [],
+            [{"x": 3, "y": 3.3}],
+            [
+                {"x": 4, "y": 4.4},
+                {"x": 5, "y": 5.5},
+                {"x": 6, "y": 6.6},
+            ],
+        ],
+        with_name="VectorTwoDAgainAgain",
+        behavior=ak.behavior,
+    )
+    # add method works but the binary operator does not
+    assert v.add(v) == v_added
+    with pytest.raises(TypeError):
+        v + v
+
+    # instead of registering every operator again, just copy the behaviors of
+    # another class to this class
+    ak.behavior.update(
+        ak._util.copy_behaviors(VectorTwoDAgain, VectorTwoDAgainAgain, ak.behavior)
+    )
+    assert v + v == v_added