⚡️ Speed up function _pad_version by 160%

[codeflash-ai]

📄 160% (1.60x) speedup for _pad_version in src/packaging/specifiers.py

⏱️ Runtime : 1.42 milliseconds → 545 microseconds (best of 6 runs)

📝 Explanation and details

The optimized code achieves a 159% speedup by eliminating expensive iterator operations and reducing memory allocations.

Key Optimizations

1. Replaced itertools.takewhile with simple loops
The original code uses itertools.takewhile(lambda x: x.isdigit(), left) which creates an iterator, then converts it to a list. The optimized version uses a straightforward loop to find the split index directly, avoiding iterator creation and list conversion overhead.

2. Eliminated intermediate list structures
The original code creates left_split and right_split lists with multiple append/insert operations, then flattens them with itertools.chain.from_iterable. The optimized version constructs the output directly using list slicing and concatenation in a single operation.

3. Added early return for equal-length case
When both release segments are the same length (no padding needed), the optimized code returns the original lists immediately. This avoids unnecessary list construction in approximately 5% of cases (based on test results showing 25/519 equal cases).

4. Conditional padding logic
Instead of always creating padding arrays for both lists, the optimized code determines which list needs padding and constructs only the necessary result.

Performance Impact

The optimization is particularly effective for:

• Lists with no leading digits (4000%+ faster): Early detection of empty release segments allows immediate return
• Equal-length release segments (200-300% faster): Early return optimization eliminates all unnecessary work
• Large lists with mismatched release segments (100-150% faster): Single-pass construction reduces overhead

Context from Function References

The function is called from _compare_equal in version specifier comparison logic, specifically for prefix matching (e.g., "1.2.*"). This is likely a hot path during dependency resolution where the same version comparisons may occur repeatedly. The optimization reduces overhead in this critical path, especially beneficial when:

• Comparing many package versions during dependency resolution
• The release segments are equal length (common case for semver-style versions)
• Processing large dependency graphs where the cumulative effect is significant

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 48 Passed
⏪ Replay Tests	✅ 255 Passed
🔎 Concolic Coverage Tests	✅ 1 Passed
📊 Tests Coverage	100.0%

🌀 Click to see Generated Regression Tests

import itertools

# imports
import pytest  # used for our unit tests
from src.packaging.specifiers import _pad_version

# unit tests

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

def test_basic_equal_length_numeric():
    # Both lists have equal length numeric segments
    left = ["1", "2", "3"]
    right = ["4", "5", "6"]
    padded_left, padded_right = _pad_version(left, right) # 4.79μs -> 1.38μs (249% faster)

def test_basic_left_shorter_numeric():
    # Left list is shorter in numeric segment
    left = ["1", "2"]
    right = ["3", "4", "5"]
    padded_left, padded_right = _pad_version(left, right) # 4.21μs -> 1.92μs (120% faster)

def test_basic_right_shorter_numeric():
    # Right list is shorter in numeric segment
    left = ["1", "2", "3"]
    right = ["4", "5"]
    padded_left, padded_right = _pad_version(left, right) # 3.79μs -> 1.50μs (153% faster)

def test_basic_non_numeric_suffix():
    # Both lists have non-numeric suffixes
    left = ["1", "2", "a"]
    right = ["3", "4", "b"]
    padded_left, padded_right = _pad_version(left, right) # 3.92μs -> 958ns (309% faster)

def test_basic_mixed_numeric_and_non_numeric():
    # Lists with mixed numeric and non-numeric values
    left = ["1", "beta"]
    right = ["2", "alpha"]
    padded_left, padded_right = _pad_version(left, right) # 3.75μs -> 833ns (350% faster)

# -------------------- EDGE TEST CASES --------------------

def test_edge_left_empty():
    # Left list is empty
    left = []
    right = ["1", "2", "3"]
    padded_left, padded_right = _pad_version(left, right) # 3.79μs -> 1.50μs (153% faster)

def test_edge_right_empty():
    # Right list is empty
    left = ["1", "2", "3"]
    right = []
    padded_left, padded_right = _pad_version(left, right) # 3.54μs -> 1.33μs (166% faster)

def test_edge_both_empty():
    # Both lists are empty
    left = []
    right = []
    padded_left, padded_right = _pad_version(left, right) # 3.17μs -> 500ns (533% faster)

def test_edge_non_numeric_leading():
    # Lists start with non-numeric values
    left = ["a", "1", "2"]
    right = ["b", "3", "4"]
    padded_left, padded_right = _pad_version(left, right) # 3.75μs -> 625ns (500% faster)

def test_edge_only_non_numeric():
    # Lists contain only non-numeric values
    left = ["alpha", "beta"]
    right = ["gamma", "delta"]
    padded_left, padded_right = _pad_version(left, right) # 3.46μs -> 583ns (493% faster)

def test_edge_numeric_then_non_numeric():
    # Numeric segment followed by non-numeric segment, with different lengths
    left = ["1", "2", "rc1"]
    right = ["3", "rc2"]
    padded_left, padded_right = _pad_version(left, right) # 3.75μs -> 1.50μs (150% faster)

def test_edge_one_numeric_one_non_numeric():
    # One list is all numeric, the other all non-numeric
    left = ["1", "2", "3"]
    right = ["a", "b", "c"]
    padded_left, padded_right = _pad_version(left, right) # 3.75μs -> 1.38μs (173% faster)

def test_edge_numeric_segment_with_leading_zeros():
    # Numeric segments with leading zeros
    left = ["01", "02"]
    right = ["1", "2", "3"]
    padded_left, padded_right = _pad_version(left, right) # 3.58μs -> 1.50μs (139% faster)

def test_edge_non_numeric_in_numeric_segment():
    # Non-numeric value in the middle of what looks like numeric segment
    left = ["1", "a", "2"]
    right = ["3", "4", "b"]
    padded_left, padded_right = _pad_version(left, right) # 3.67μs -> 1.42μs (159% faster)

def test_edge_numeric_segment_with_negative_numbers():
    # Negative numbers are not considered digits by isdigit()
    left = ["-1", "2"]
    right = ["3", "4"]
    padded_left, padded_right = _pad_version(left, right) # 3.83μs -> 1.50μs (156% faster)

def test_edge_numeric_segment_with_empty_strings():
    # Empty strings are not digits
    left = ["", "1", "2"]
    right = ["3", "4"]
    padded_left, padded_right = _pad_version(left, right) # 3.67μs -> 1.29μs (184% faster)

def test_edge_numeric_segment_with_spaces():
    # Strings with spaces are not digits
    left = ["1", " ", "2"]
    right = ["3", "4"]
    padded_left, padded_right = _pad_version(left, right) # 3.58μs -> 1.29μs (178% faster)

# -------------------- LARGE SCALE TEST CASES --------------------

def test_large_scale_equal_length():
    # Large numeric segments of equal length
    left = [str(i) for i in range(500)]
    right = [str(i) for i in range(500, 1000)]
    padded_left, padded_right = _pad_version(left, right) # 64.5μs -> 27.4μs (135% faster)

def test_large_scale_left_shorter():
    # Left numeric segment is shorter
    left = [str(i) for i in range(250)]
    right = [str(i) for i in range(500)]
    padded_left, padded_right = _pad_version(left, right) # 48.9μs -> 23.5μs (108% faster)

def test_large_scale_right_shorter():
    # Right numeric segment is shorter
    left = [str(i) for i in range(500)]
    right = [str(i) for i in range(250)]
    padded_left, padded_right = _pad_version(left, right) # 47.7μs -> 23.1μs (106% faster)

def test_large_scale_non_numeric_suffix():
    # Large numeric segments with non-numeric suffixes
    left = [str(i) for i in range(500)] + ["rc1"]
    right = [str(i) for i in range(500)] + ["rc2"]
    padded_left, padded_right = _pad_version(left, right) # 58.0μs -> 27.3μs (113% faster)

def test_large_scale_all_non_numeric():
    # Large non-numeric lists
    left = ["a"] * 1000
    right = ["b"] * 1000
    padded_left, padded_right = _pad_version(left, right) # 27.4μs -> 625ns (4287% faster)

def test_large_scale_left_empty():
    # Large right, left empty
    left = []
    right = [str(i) for i in range(1000)]
    padded_left, padded_right = _pad_version(left, right) # 67.8μs -> 32.4μs (109% faster)

def test_large_scale_right_empty():
    # Large left, right empty
    left = [str(i) for i in range(1000)]
    right = []
    padded_left, padded_right = _pad_version(left, right) # 66.7μs -> 32.7μs (104% faster)

def test_large_scale_mixed_numeric_and_non_numeric():
    # Large numeric segment, then non-numeric suffix
    left = [str(i) for i in range(500)] + ["alpha"] * 500
    right = [str(i) for i in range(400)] + ["beta"] * 600
    padded_left, padded_right = _pad_version(left, right) # 65.7μs -> 30.0μs (119% faster)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.

import itertools

# imports
import pytest  # used for our unit tests
from src.packaging.specifiers import _pad_version

# unit tests

# --- Basic Test Cases ---

def test_equal_length_release_segments():
    # Both lists have same number of leading digits
    left = ["1", "2", "3", "a", "b"]
    right = ["4", "5", "6", "c", "d"]
    padded_left, padded_right = _pad_version(left, right) # 3.88μs -> 1.00μs (288% faster)

def test_left_shorter_release_segment():
    # Left has fewer leading digits than right
    left = ["1", "2", "a"]
    right = ["4", "5", "6", "b"]
    padded_left, padded_right = _pad_version(left, right) # 3.75μs -> 1.50μs (150% faster)

def test_right_shorter_release_segment():
    # Right has fewer leading digits than left
    left = ["1", "2", "3", "a"]
    right = ["4", "b"]
    padded_left, padded_right = _pad_version(left, right) # 3.62μs -> 1.42μs (156% faster)

def test_no_release_segment():
    # Neither list starts with a digit
    left = ["a", "b"]
    right = ["c", "d"]
    padded_left, padded_right = _pad_version(left, right) # 3.50μs -> 583ns (500% faster)

def test_one_empty_list():
    # One list is empty
    left = []
    right = ["1", "2", "a"]
    padded_left, padded_right = _pad_version(left, right) # 3.67μs -> 1.29μs (184% faster)

def test_both_empty_lists():
    # Both lists are empty
    left = []
    right = []
    padded_left, padded_right = _pad_version(left, right) # 3.12μs -> 500ns (525% faster)

# --- Edge Test Cases ---

def test_left_all_digits_right_none():
    # Left is all digits, right is all non-digits
    left = ["1", "2", "3"]
    right = ["a", "b", "c"]
    padded_left, padded_right = _pad_version(left, right) # 3.88μs -> 1.42μs (174% faster)

def test_right_all_digits_left_none():
    # Right is all digits, left is all non-digits
    left = ["x", "y"]
    right = ["4", "5"]
    padded_left, padded_right = _pad_version(left, right) # 3.62μs -> 1.29μs (181% faster)

def test_release_segment_with_zero():
    # Release segment contains zero
    left = ["0", "a"]
    right = ["0", "b"]
    padded_left, padded_right = _pad_version(left, right) # 3.46μs -> 708ns (388% faster)

def test_non_digit_in_release_segment():
    # Release segment interrupted by non-digit
    left = ["1", "a", "2"]
    right = ["2", "b", "3"]
    padded_left, padded_right = _pad_version(left, right) # 3.38μs -> 667ns (406% faster)

def test_long_non_digit_suffix():
    # Long non-digit suffix after release segment
    left = ["1", "2", "x", "y", "z"]
    right = ["3", "4", "a", "b", "c"]
    padded_left, padded_right = _pad_version(left, right) # 3.54μs -> 667ns (431% faster)

def test_release_segment_with_leading_zeros():
    # Release segment with leading zeros
    left = ["0", "1", "a"]
    right = ["0", "1", "b"]
    padded_left, padded_right = _pad_version(left, right) # 3.46μs -> 708ns (389% faster)

def test_release_segment_none_both():
    # Both lists have no digits at all
    left = ["x", "y", "z"]
    right = ["a", "b", "c"]
    padded_left, padded_right = _pad_version(left, right) # 3.46μs -> 625ns (453% faster)

def test_release_segment_partial_digits():
    # Digits not at start should not be counted
    left = ["a", "1", "2"]
    right = ["b", "2", "3"]
    padded_left, padded_right = _pad_version(left, right) # 3.29μs -> 541ns (509% faster)

def test_release_segment_empty_suffix():
    # Suffix is empty after digits
    left = ["1", "2"]
    right = ["3", "4"]
    padded_left, padded_right = _pad_version(left, right) # 3.38μs -> 667ns (406% faster)

def test_release_segment_suffix_longer():
    # Suffix is longer in one list
    left = ["1", "a", "b", "c"]
    right = ["2", "b"]
    padded_left, padded_right = _pad_version(left, right) # 3.46μs -> 667ns (418% faster)

# --- Large Scale Test Cases ---

def test_large_equal_release_segment():
    # Both lists have large, equal-length release segments
    left = [str(i) for i in range(500)] + ["a"]
    right = [str(i) for i in range(500)] + ["b"]
    padded_left, padded_right = _pad_version(left, right) # 59.5μs -> 27.2μs (119% faster)

def test_large_left_shorter_release_segment():
    # Left has shorter release segment than right
    left = [str(i) for i in range(250)] + ["x"]
    right = [str(i) for i in range(500)] + ["y"]
    padded_left, padded_right = _pad_version(left, right) # 47.6μs -> 23.1μs (106% faster)

def test_large_right_shorter_release_segment():
    # Right has shorter release segment than left
    left = [str(i) for i in range(500)] + ["x"]
    right = [str(i) for i in range(250)] + ["y"]
    padded_left, padded_right = _pad_version(left, right) # 47.3μs -> 22.3μs (112% faster)

def test_large_no_release_segment():
    # Large lists with no digits at start
    left = ["a"] * 1000
    right = ["b"] * 1000
    padded_left, padded_right = _pad_version(left, right) # 24.2μs -> 542ns (4374% faster)

def test_large_one_empty():
    # One large list, one empty
    left = []
    right = [str(i) for i in range(999)] + ["z"]
    padded_left, padded_right = _pad_version(left, right) # 66.5μs -> 32.5μs (105% faster)

def test_large_both_empty():
    # Both lists empty
    left = []
    right = []
    padded_left, padded_right = _pad_version(left, right) # 3.21μs -> 458ns (600% faster)

def test_large_non_digit_suffix():
    # Large release segment, large non-digit suffix
    left = [str(i) for i in range(500)] + ["x"] * 499
    right = [str(i) for i in range(500)] + ["y"] * 499
    padded_left, padded_right = _pad_version(left, right) # 67.8μs -> 27.0μs (151% faster)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.

from src.packaging.specifiers import _pad_version

def test__pad_version():
    _pad_version([], [])

⏪ Click to see Replay Tests

Test File::Test Function	Original ⏱️	Optimized ⏱️	Speedup
test_benchmark_py__replay_test_0.py::test_src_packaging_specifiers__pad_version	523μs	178μs	193%✅

🔎 Click to see Concolic Coverage Tests

Test File::Test Function	Original ⏱️	Optimized ⏱️	Speedup
codeflash_concolic_ui1l843q/tmp6v1_j8no/test_concolic_coverage.py::test__pad_version	8.29μs	917ns	804%✅

To edit these changes git checkout codeflash/optimize-_pad_version-mjjljaqd and push.