⚡️ Speed up method HiddenKeyDict.__len__ by 63%

[codeflash-ai]

📄 63% (0.63x) speedup for HiddenKeyDict.__len__ in xarray/core/utils.py

⏱️ Runtime : 3.59 microseconds → 2.21 microseconds (best of 45 runs)

📝 Explanation and details

The optimization replaces a set intersection operation with an explicit loop and membership check, resulting in a 62% speedup.

Key changes:

• Original: num_hidden = len(self._hidden_keys & self._data.keys()) - creates a set intersection between hidden keys and data keys, then counts the result
• Optimized: Iterates through self._hidden_keys and counts how many exist in self._data using key in self._data

Why this is faster:

1. Avoids intermediate set creation: The original approach creates a new set from the intersection operation, which requires memory allocation and set construction overhead
2. Eliminates .keys() call: The original must materialize all dictionary keys into a set-like view, while the optimized version only checks individual key membership
3. Short-circuits early: When checking key in self._data, Python can stop as soon as it finds/doesn't find the key, rather than building complete sets first
4. Reduces memory pressure: No temporary set objects are created, leading to better cache locality and reduced GC pressure

Performance characteristics:
This optimization is particularly effective when:

• The number of hidden keys is small relative to the total data size (common case)
• Dictionary lookups are faster than set operations for the given key types
• Memory allocation overhead is significant compared to the computational work

The 62% speedup demonstrates that set intersection operations have substantial overhead compared to simple dictionary membership checks in typical usage patterns.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 1 Passed
⏪ Replay Tests	✅ 1 Passed
🔎 Concolic Coverage Tests	🔘 None Found
📊 Tests Coverage	100.0%

🌀 Generated Regression Tests and Runtime

from collections.abc import Iterator, MutableMapping
from typing import Any, Iterable, TypeVar

# imports
import pytest
from xarray.core.utils import HiddenKeyDict

K = TypeVar("K")
V = TypeVar("V")
from xarray.core.utils import HiddenKeyDict

# unit tests

# ----------- BASIC TEST CASES -----------


def test_len_dict_with_unhashable_key():
    # Test: Dict with unhashable key (should raise TypeError)
    with pytest.raises(TypeError):
        HiddenKeyDict({["a"]: 1}, ["a"])  # list is unhashable

from xarray.core.utils import HiddenKeyDict

def test_HiddenKeyDict___len__():
    HiddenKeyDict.__len__(HiddenKeyDict({}, ()))

Timer unit: 1e-09 s

⏪ 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_core_utils_HiddenKeyDict___len__	3.59μs	2.21μs	62.6%✅

To edit these changes git checkout codeflash/optimize-HiddenKeyDict.__len__-mj9vz41t and push.