⚡️ Speed up method LRUCache.popitem by 45%

[codeflash-ai]

📄 45% (0.45x) speedup for LRUCache.popitem in electrum/lrucache.py

⏱️ Runtime : 504 microseconds → 348 microseconds (best of 250 runs)

📝 Explanation and details

The optimization achieves a 44% speedup by caching the self.__data dictionary reference in a local variable within the pop method.

What changed:

• Added data = self.__data at the start of the pop method
• Changed if key in self: to if key in data:
• Changed value = self[key] to value = data[key]

Why this is faster:
The original code performed two expensive operations for each pop call:

1. key in self triggered the __contains__ method, which internally accessed self.__data
2. self[key] triggered the __getitem__ method, which also accessed self.__data and called the LRU update mechanism

By caching self.__data in a local variable, the optimization:

• Eliminates method call overhead - Direct dictionary access (key in data) is much faster than going through __contains__
• Removes LRU update overhead - data[key] bypasses the __getitem__ method that would unnecessarily update the LRU order during a pop operation
• Reduces attribute lookups - Local variable access is faster than repeated self.__data lookups

Performance impact:
The line profiler shows the most significant improvement in value = self[key] (1.125ms → 0.118ms, ~90% faster) because it eliminates the costly LRU update that was happening unnecessarily during pop operations. The if key in self check also improved substantially (0.3ms → 0.108ms).

Test case benefits:
This optimization particularly benefits workloads with frequent cache evictions, as evidenced by the large-scale tests showing 47-51% improvements. The optimization is most effective when popitem() is called frequently, which happens during cache eviction scenarios when the cache reaches its maximum size.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 598 Passed
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	✅ 3 Passed
📊 Tests Coverage	100.0%

🌀 Generated Regression Tests and Runtime

import collections
import collections.abc
from typing import TypeVar

# imports
import pytest  # used for our unit tests
from electrum.lrucache import LRUCache

_KT = TypeVar("_KT")
_VT = TypeVar("_VT")
from electrum.lrucache import LRUCache

# unit tests

# ---- Basic Test Cases ----

def test_popitem_basic_single_element():
    # Test popitem on a cache with one item
    cache = LRUCache(maxsize=2)
    cache['a'] = 1
    codeflash_output = cache.popitem() # 2.75μs -> 2.07μs (32.8% faster)
    # After popping, popitem should raise KeyError
    with pytest.raises(KeyError):
        cache.popitem() # 1.51μs -> 1.50μs (0.600% faster)

def test_popitem_basic_multiple_elements():
    # Test popitem returns the least recently used item
    cache = LRUCache(maxsize=3)
    cache['a'] = 1
    cache['b'] = 2
    cache['c'] = 3
    # Access 'a' and 'b' to update their usage
    _ = cache['a']
    _ = cache['b']
    # Now 'c' is LRU
    codeflash_output = cache.popitem() # 2.12μs -> 1.60μs (32.2% faster)

def test_popitem_basic_usage_update():
    # Test that accessing an item updates its usage
    cache = LRUCache(maxsize=3)
    cache['x'] = 10
    cache['y'] = 20
    cache['z'] = 30
    # Access 'x', now 'y' is LRU
    _ = cache['x']
    codeflash_output = cache.popitem() # 2.07μs -> 1.78μs (16.5% faster)

def test_popitem_basic_insertion_order():
    # Test that insertion order is respected until usage changes
    cache = LRUCache(maxsize=3)
    cache['a'] = 1
    cache['b'] = 2
    cache['c'] = 3
    # No access, so 'a' is LRU
    codeflash_output = cache.popitem() # 2.25μs -> 1.78μs (26.2% faster)

# ---- Edge Test Cases ----

def test_popitem_empty_cache():
    # Test popitem on an empty cache raises KeyError
    cache = LRUCache(maxsize=1)
    with pytest.raises(KeyError):
        cache.popitem() # 1.72μs -> 1.76μs (1.93% slower)

def test_popitem_repeated_pop_until_empty():
    # Test repeated popitem calls until cache is empty
    cache = LRUCache(maxsize=2)
    cache['foo'] = 'bar'
    cache['baz'] = 'qux'
    # First pop removes 'foo' (LRU)
    codeflash_output = cache.popitem() # 2.58μs -> 1.89μs (36.1% faster)
    # Second pop removes 'baz'
    codeflash_output = cache.popitem() # 1.54μs -> 1.18μs (31.0% faster)
    # Third pop raises KeyError
    with pytest.raises(KeyError):
        cache.popitem() # 1.41μs -> 1.40μs (0.928% faster)

def test_popitem_after_eviction():
    # Test popitem after automatic eviction due to maxsize
    cache = LRUCache(maxsize=2)
    cache['a'] = 1
    cache['b'] = 2
    cache['c'] = 3  # Should evict 'a' (LRU)
    # Now 'b' is LRU
    codeflash_output = cache.popitem() # 1.67μs -> 1.20μs (39.5% faster)

def test_popitem_with_custom_getsizeof():
    # Test popitem with custom getsizeof function
    def getsizeof(value):
        return len(str(value))
    cache = LRUCache(maxsize=5, getsizeof=getsizeof)
    cache['a'] = '12'  # size 2
    cache['b'] = '345' # size 3
    # Both fit, total size 5
    codeflash_output = cache.popitem() # 2.26μs -> 1.71μs (32.5% faster)

def test_popitem_eviction_with_custom_getsizeof():
    # Test eviction order with custom getsizeof
    def getsizeof(value):
        return value
    cache = LRUCache(maxsize=5, getsizeof=getsizeof)
    cache['x'] = 2
    cache['y'] = 2
    cache['z'] = 2  # Should evict 'x' (LRU)
    codeflash_output = cache.popitem() # 1.60μs -> 1.22μs (31.8% faster)

def test_popitem_after_access_and_deletion():
    # Test popitem after accessing and deleting items
    cache = LRUCache(maxsize=3)
    cache['a'] = 1
    cache['b'] = 2
    cache['c'] = 3
    _ = cache['b']  # Update usage
    del cache['a']
    # Now 'c' is LRU
    codeflash_output = cache.popitem() # 1.96μs -> 1.46μs (34.7% faster)

def test_popitem_with_non_str_keys():
    # Test popitem works with non-string keys
    cache = LRUCache(maxsize=3)
    cache[1] = 'one'
    cache[(2, 3)] = 'tuple'
    cache[None] = 'none'
    # 1 is LRU
    codeflash_output = cache.popitem() # 2.29μs -> 1.74μs (31.2% faster)

def test_popitem_with_mutable_values():
    # Test popitem with mutable values
    cache = LRUCache(maxsize=3)
    cache['list'] = [1, 2, 3]
    cache['dict'] = {'a': 1}
    cache['set'] = {1, 2}
    # 'list' is LRU
    codeflash_output = cache.popitem() # 2.25μs -> 1.69μs (33.5% faster)

def test_popitem_eviction_on_large_value():
    # Test eviction when inserting a value that exceeds maxsize
    cache = LRUCache(maxsize=2)
    with pytest.raises(ValueError):
        cache['big'] = 'x' * 10  # getsizeof returns 1, so no error, but let's try with custom getsizeof
    cache = LRUCache(maxsize=2, getsizeof=lambda v: 3)
    with pytest.raises(ValueError):
        cache['big'] = 'xxx'

# ---- Large Scale Test Cases ----

def test_popitem_large_scale_eviction_order():
    # Test eviction order with many items
    cache = LRUCache(maxsize=100)
    for i in range(100):
        cache[i] = i
    # Access most recent 10 items to update their usage
    for i in range(90, 100):
        _ = cache[i]
    # Now pop 90 items, should get 0..89 in order
    for i in range(90):
        key, value = cache.popitem() # 80.1μs -> 54.3μs (47.5% faster)

def test_popitem_large_scale_access_pattern():
    # Test that popitem respects access pattern in large cache
    cache = LRUCache(maxsize=50)
    for i in range(50):
        cache[i] = i
    # Access all even keys to mark them as recently used
    for i in range(0, 50, 2):
        _ = cache[i]
    # Now pop 25 items, should get all odd keys first
    odd_keys = set(range(1, 50, 2))
    popped_keys = set()
    for _ in range(25):
        key, value = cache.popitem() # 22.5μs -> 15.3μs (46.6% faster)
        popped_keys.add(key)

def test_popitem_large_scale_full_eviction():
    # Test full eviction via popitem in large cache
    cache = LRUCache(maxsize=200)
    for i in range(200):
        cache[i] = i
    popped = []
    for _ in range(200):
        key, value = cache.popitem() # 174μs -> 116μs (49.4% faster)
        popped.append((key, value))
    # All keys should have been popped, in insertion order
    keys, values = zip(*popped)
    with pytest.raises(KeyError):
        cache.popitem() # 1.80μs -> 1.79μs (0.446% faster)

def test_popitem_large_scale_with_custom_getsizeof():
    # Test large scale with custom getsizeof
    def getsizeof(value):
        return 2
    cache = LRUCache(maxsize=100, getsizeof=getsizeof)
    for i in range(50):  # Each item size 2, so 50 items fit
        cache[i] = i
    # Pop all items
    for i in range(50):
        key, value = cache.popitem() # 45.1μs -> 29.8μs (51.2% faster)

def test_popitem_large_scale_eviction_and_usage_update():
    # Test eviction and usage update in large cache
    cache = LRUCache(maxsize=100)
    for i in range(100):
        cache[i] = i
    # Access keys 0-49 to update their usage
    for i in range(50):
        _ = cache[i]
    # Insert 10 more items, which should evict keys 50-59 (LRU)
    for i in range(100, 110):
        cache[i] = i
    # Now keys 50-59 should be gone
    for i in range(50, 60):
        pass
    # Pop 10 items, should get 60-69
    for i in range(60, 70):
        key, value = cache.popitem() # 8.93μs -> 5.96μs (49.9% faster)
    # Remaining keys: 0-49, 70-109
    expected_keys = set(range(0, 50)) | set(range(70, 110))
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.

import collections
import collections.abc
from typing import TypeVar

# imports
import pytest
from electrum.lrucache import LRUCache

_KT = TypeVar("_KT")
_VT = TypeVar("_VT")
from electrum.lrucache import LRUCache

# unit tests

# ---- Basic Test Cases ----

def test_popitem_basic_lru_order():
    # Test that popitem removes and returns the least recently used item
    cache = LRUCache(maxsize=3)
    cache['a'] = 1
    cache['b'] = 2
    cache['c'] = 3
    # Access 'a' to make it most recently used
    _ = cache['a']
    # Now 'b' is least recently used
    key, value = cache.popitem() # 2.47μs -> 2.10μs (17.5% faster)

def test_popitem_basic_empty_cache():
    # Test that popitem raises KeyError on empty cache
    cache = LRUCache(maxsize=2)
    with pytest.raises(KeyError):
        cache.popitem() # 1.83μs -> 1.84μs (0.218% slower)

def test_popitem_basic_single_item():
    # Test popitem when only one item is present
    cache = LRUCache(maxsize=1)
    cache['x'] = 42
    key, value = cache.popitem() # 2.82μs -> 2.23μs (26.1% faster)

def test_popitem_basic_multiple_calls():
    # Test popitem repeatedly until cache is empty
    cache = LRUCache(maxsize=3)
    cache['a'] = 1
    cache['b'] = 2
    cache['c'] = 3
    items = []
    for _ in range(3):
        items.append(cache.popitem()) # 5.13μs -> 3.72μs (37.9% faster)
    with pytest.raises(KeyError):
        cache.popitem() # 1.47μs -> 1.47μs (0.136% slower)

# ---- Edge Test Cases ----

def test_popitem_edge_access_updates_lru():
    # Test that accessing an item updates its LRU status
    cache = LRUCache(maxsize=3)
    cache['x'] = 1
    cache['y'] = 2
    cache['z'] = 3
    # Access 'x' and 'y'
    _ = cache['x']
    _ = cache['y']
    # Now 'z' should be LRU
    key, value = cache.popitem() # 2.02μs -> 1.84μs (9.50% faster)

def test_popitem_edge_setitem_updates_lru():
    # Test that setting an existing key updates its LRU status
    cache = LRUCache(maxsize=3)
    cache['a'] = 1
    cache['b'] = 2
    cache['c'] = 3
    cache['a'] = 100  # Update 'a', now 'b' is LRU
    key, value = cache.popitem() # 2.14μs -> 1.64μs (30.0% faster)

def test_popitem_edge_delitem_then_popitem():
    # Test that deleting an item updates the order correctly
    cache = LRUCache(maxsize=3)
    cache['a'] = 1
    cache['b'] = 2
    cache['c'] = 3
    del cache['b']
    key, value = cache.popitem() # 2.25μs -> 1.55μs (45.1% faster)

def test_popitem_edge_eviction_on_setitem():
    # Test that popitem is called internally when inserting over maxsize
    cache = LRUCache(maxsize=2)
    cache['a'] = 1
    cache['b'] = 2
    cache['c'] = 3  # Should evict 'a'
    key, value = cache.popitem() # 1.65μs -> 1.21μs (36.5% faster)

def test_popitem_edge_custom_getsizeof():
    # Test with custom getsizeof function
    def getsizeof(x):
        return len(str(x))
    cache = LRUCache(maxsize=5, getsizeof=getsizeof)
    cache['a'] = '12'  # size 2
    cache['b'] = '345' # size 3
    # Adding 'c' with size 1 should fit
    cache['c'] = 'x'   # size 1, total size now 6, should evict 'a'
    key, value = cache.popitem() # 1.69μs -> 1.19μs (41.9% faster)

def test_popitem_edge_value_too_large():
    # Test inserting a value larger than maxsize
    cache = LRUCache(maxsize=1)
    with pytest.raises(ValueError):
        cache['big'] = 'x'*10

def test_popitem_edge_eviction_order_with_access():
    # Test eviction order after access patterns
    cache = LRUCache(maxsize=3)
    cache['a'] = 1
    cache['b'] = 2
    cache['c'] = 3
    _ = cache['a']
    cache['d'] = 4  # Should evict 'b'

# ---- Large Scale Test Cases ----

def test_popitem_large_scale_eviction():
    # Fill cache to maxsize and test popitem order
    cache = LRUCache(maxsize=100)
    for i in range(100):
        cache[i] = i
    # Access some items to update their LRU status
    for i in range(90, 100):
        _ = cache[i]
    # Now, items 0..89 are LRU, pop them all and check order
    for i in range(90):
        key, value = cache.popitem() # 79.2μs -> 53.4μs (48.4% faster)

def test_popitem_large_scale_performance():
    # Test popitem performance and correctness with 1000 items
    cache = LRUCache(maxsize=1000)
    for i in range(1000):
        cache[i] = i
    # Pop 10 items and verify order
    for i in range(10):
        key, value = cache.popitem() # 11.0μs -> 7.64μs (44.2% faster)

def test_popitem_large_scale_eviction_on_insert():
    # Test eviction when inserting over maxsize in large cache
    cache = LRUCache(maxsize=100)
    for i in range(100):
        cache[i] = i
    # Insert 10 more, should evict 0..9
    for i in range(100, 110):
        cache[i] = i
    # Popitem should return 10 as next LRU
    key, value = cache.popitem() # 1.11μs -> 811ns (37.0% faster)

def test_popitem_large_scale_access_pattern():
    # Test LRU order after random access pattern
    cache = LRUCache(maxsize=50)
    for i in range(50):
        cache[i] = i
    # Access items 25..49 to update their LRU status
    for i in range(25, 50):
        _ = cache[i]
    # Pop 25 items, should be 0..24
    for i in range(25):
        key, value = cache.popitem() # 22.5μs -> 15.3μs (47.3% faster)

def test_popitem_large_scale_empty_pop():
    # Test popitem on empty large cache
    cache = LRUCache(maxsize=500)
    with pytest.raises(KeyError):
        cache.popitem() # 1.93μs -> 1.94μs (0.103% slower)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.

from electrum.lrucache import LRUCache
import pytest

def test_LRUCache_popitem():
    with pytest.raises(KeyError, match="'LRUCache\\ is\\ empty'"):
        LRUCache.popitem(LRUCache(0, getsizeof=0))

🔎 Concolic Coverage Tests and Runtime

Test File::Test Function	Original ⏱️	Optimized ⏱️	Speedup
codeflash_concolic_6p7ovzz5/tmpvq76lt4m/test_concolic_coverage.py::test_LRUCache_popitem	1.84μs	1.91μs	-3.87%⚠️

To edit these changes git checkout codeflash/optimize-LRUCache.popitem-mhx8u5tg and push.