⚡️ Speed up method CFTimeIndex.__repr__ by 23%

[codeflash-ai]

📄 23% (0.23x) speedup for CFTimeIndex.__repr__ in xarray/coding/cftimeindex.py

⏱️ Runtime : 61.0 microseconds → 49.4 microseconds (best of 10 runs)

📝 Explanation and details

The optimized code achieves a 23% speedup through several key performance improvements focused on reducing string operations overhead and eliminating redundant computations:

Key Optimizations:

1. Eliminated quadratic string concatenation: The original format_times built the result string through repeated concatenation (representation += format_row(...)), which creates new string objects each time. The optimized version accumulates parts in a list and uses a single "".join(parts) call, reducing time complexity from O(n²) to O(n).

2. Streamlined format_attrs: Replaced dictionary creation and list comprehension with a direct tuple of formatted strings, eliminating intermediate data structures and reducing the number of join operations.

3. Added format_row function: This separates row formatting logic and includes an early return for empty inputs, avoiding unnecessary string operations when no data is present.

4. Optimized mathematical operations:

   • Replaced math.ceil(len(index) / n_per_row) with integer arithmetic (n + n_per_row - 1) // n_per_row
   • Pre-computed per_elem_width = CFTIME_REPR_LENGTH + len(separator) to avoid repeated calculations
   • Added early return for empty index case

5. Improved slicing efficiency: Used min((row + 1) * n_per_row, n) to avoid out-of-bounds slicing and cached len(self) and self.values in local variables.

Performance Impact:
These optimizations are particularly effective for CFTimeIndex objects with many elements, where string formatting becomes a bottleneck. The improvements reduce both CPU cycles and memory allocations, especially beneficial when __repr__ is called frequently during debugging, logging, or interactive data exploration in scientific computing workflows typical of xarray usage.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	🔘 None Found
⏪ Replay Tests	✅ 1 Passed
🔎 Concolic Coverage Tests	🔘 None Found
📊 Tests Coverage	60.0%

⏪ Replay Tests and Runtime

Test File::Test Function	Original ⏱️	Optimized ⏱️	Speedup
test_pytest_xarrayteststest_concat_py_xarrayteststest_computation_py_xarrayteststest_formatting_py_xarray__replay_test_0.py::test_xarray_coding_cftimeindex_CFTimeIndex___repr__	61.0μs	49.4μs	23.4%✅

To edit these changes git checkout codeflash/optimize-CFTimeIndex.__repr__-mir2imwj and push.