perf: fix O(T²) list copies in CopyVisitor.addition#189
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The default `addition` in ExpressionVisitorOperations accumulated results with `res = res + o` in a loop. The flattening `__add__` on ExpressionNode copies the accumulated operand list at each step, giving O(T²) total copy work for a T-term AdditionNode. Override `addition` in CopyVisitor to build the AdditionNode directly from a list comprehension, reducing the cost to O(T). Add a regression test that asserts the time ratio between T=10_000 and T=1_000 stays below 20 (linear ≈ 10, quadratic ≈ 100). Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
aoustry
approved these changes
Mar 25, 2026
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Summary
CopyVisitorinherited the defaultaddition()fromExpressionVisitorOperations, which accumulated visited operands withres = res + oin a loop. The flattening__add__onExpressionNodecopies the accumulated operand list at each step, giving O(T²) total list copies for a T-termAdditionNode.addition()inCopyVisitorto build theAdditionNodedirectly from a list comprehension — O(T).This is Fix 2 from the superlinear complexity analysis (see issue #188).
Test plan
pytest tests/unittests/expressions/visitor/test_copy.py— both tests pass, including the newtest_copy_large_addition_is_linearpytest tests/passes🤖 Generated with Claude Code