⚡️ Speed up method Stack.empty by 20%

[codeflash-ai]

📄 20% (0.20x) speedup for Stack.empty in guardrails/classes/generic/stack.py

⏱️ Runtime : 228 microseconds → 189 microseconds (best of 67 runs)

📝 Explanation and details

The optimized code achieves a 20% speedup by replacing len(self) == 0 with not self in the empty() method. This optimization leverages Python's built-in truthiness evaluation mechanism.

Key Performance Improvement:

• len(self) == 0 requires calling the len() function, which internally calls __len__() on the list, counts all elements, and then performs an equality comparison
• not self directly uses the list's __bool__() method (inherited from the built-in list class), which returns False immediately if the list is empty without counting elements

Why This Works:
In Python, not self on a list object is equivalent to checking if the list is empty, but it's implemented at a lower level in the interpreter. The __bool__() method for lists simply checks if the first element exists rather than counting all elements, making it more efficient than len().

Performance Characteristics:
The optimization shows consistent improvements across all test scenarios:

• Empty stacks: 17-32% faster (best case scenarios)
• Small stacks (1-5 elements): 9-28% faster
• Large stacks (1000+ elements): 31-44% faster (most significant gains)
• Edge cases with falsy values: 12-26% faster

The performance gain is particularly pronounced with larger stacks because len() has to traverse or maintain a count of all elements, while not self only needs to check for the existence of any element.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 1098 Passed
⏪ Replay Tests	✅ 255 Passed
🔎 Concolic Coverage Tests	🔘 None Found
📊 Tests Coverage	100.0%

🌀 Generated Regression Tests and Runtime

from typing import List, TypeVar

# imports
import pytest  # used for our unit tests
from guardrails.classes.generic.stack import Stack

T = TypeVar("T")
from guardrails.classes.generic.stack import Stack

# unit tests

# -------------------------
# 1. Basic Test Cases
# -------------------------

def test_empty_stack_returns_true():
    """Test that an empty stack returns True for empty()."""
    s = Stack()
    codeflash_output = s.empty() # 559ns -> 435ns (28.5% faster)

def test_nonempty_stack_returns_false():
    """Test that a stack with one element returns False for empty()."""
    s = Stack(1)
    codeflash_output = s.empty() # 431ns -> 394ns (9.39% faster)

def test_stack_with_multiple_elements_returns_false():
    """Test that a stack with multiple elements returns False for empty()."""
    s = Stack(1, 2, 3)
    codeflash_output = s.empty() # 444ns -> 405ns (9.63% faster)

# -------------------------
# 2. Edge Test Cases
# -------------------------

def test_stack_after_pop_all_elements():
    """Test that a stack emptied by popping all elements returns True for empty()."""
    s = Stack(1, 2)
    s.pop()
    s.pop()
    codeflash_output = s.empty() # 481ns -> 388ns (24.0% faster)

def test_stack_after_append_and_pop():
    """Test that a stack after append and pop returns to empty state."""
    s = Stack()
    s.append('a')
    codeflash_output = s.empty() # 418ns -> 392ns (6.63% faster)
    s.pop()
    codeflash_output = s.empty() # 218ns -> 233ns (6.44% slower)

def test_stack_with_none_element():
    """Test that a stack initialized with None as an element is not empty."""
    s = Stack(None)
    codeflash_output = s.empty() # 442ns -> 401ns (10.2% faster)

def test_stack_with_falsey_elements():
    """Test that a stack with 0, '', or False as elements is not empty."""
    s = Stack(0, '', False)
    codeflash_output = s.empty() # 432ns -> 409ns (5.62% faster)

def test_stack_clear_method():
    """Test that using clear() makes the stack empty."""
    s = Stack(1, 2, 3)
    s.clear()
    codeflash_output = s.empty() # 461ns -> 379ns (21.6% faster)

def test_stack_after_del_slice():
    """Test that deleting all elements via slice makes the stack empty."""
    s = Stack(1, 2, 3)
    del s[:]
    codeflash_output = s.empty() # 468ns -> 391ns (19.7% faster)

def test_stack_after_del_partial_slice():
    """Test that deleting some elements via slice does not make the stack empty if elements remain."""
    s = Stack(1, 2, 3)
    del s[:2]
    codeflash_output = s.empty() # 458ns -> 374ns (22.5% faster)
    del s[:]
    codeflash_output = s.empty() # 212ns -> 188ns (12.8% faster)

def test_stack_after_extend_and_pop():
    """Test that extending and then popping all elements makes the stack empty."""
    s = Stack()
    s.extend([1, 2, 3])
    codeflash_output = s.empty() # 424ns -> 368ns (15.2% faster)
    s.pop()
    s.pop()
    s.pop()
    codeflash_output = s.empty() # 198ns -> 208ns (4.81% slower)

def test_stack_with_various_types():
    """Test that a stack with mixed types is not empty."""
    s = Stack(1, "a", None, [], {})
    codeflash_output = s.empty() # 442ns -> 392ns (12.8% faster)

# -------------------------
# 3. Large Scale Test Cases
# -------------------------

def test_large_stack_not_empty():
    """Test that a stack with 1000 elements is not empty."""
    s = Stack(*range(1000))
    codeflash_output = s.empty() # 507ns -> 383ns (32.4% faster)

def test_large_stack_becomes_empty():
    """Test that popping all elements from a large stack makes it empty."""
    s = Stack(*range(1000))
    for _ in range(1000):
        s.pop()
    codeflash_output = s.empty() # 442ns -> 336ns (31.5% faster)

def test_large_stack_clear():
    """Test that clear() on a large stack makes it empty."""
    s = Stack(*range(1000))
    s.clear()
    codeflash_output = s.empty() # 417ns -> 367ns (13.6% faster)

def test_large_stack_del_slice():
    """Test that deleting all elements via slice on a large stack makes it empty."""
    s = Stack(*range(1000))
    del s[:]
    codeflash_output = s.empty() # 429ns -> 350ns (22.6% faster)

def test_large_stack_partial_pop():
    """Test that popping some elements from a large stack does not make it empty until all are removed."""
    s = Stack(*range(1000))
    for _ in range(999):
        s.pop()
        codeflash_output = s.empty() # 138μs -> 113μs (21.9% faster)
    s.pop()
    codeflash_output = s.empty() # 153ns -> 159ns (3.77% slower)

# -------------------------
# Additional Edge Cases
# -------------------------

def test_empty_stack_after_multiple_operations():
    """Test that a stack returns to empty after several push/pop operations."""
    s = Stack()
    for i in range(10):
        s.append(i)
    for _ in range(10):
        s.pop()
    codeflash_output = s.empty() # 485ns -> 413ns (17.4% faster)

def test_stack_after_insert_and_remove():
    """Test stack after inserting and removing elements."""
    s = Stack()
    s.insert(0, 'x')
    codeflash_output = s.empty() # 431ns -> 388ns (11.1% faster)
    s.remove('x')
    codeflash_output = s.empty() # 222ns -> 187ns (18.7% faster)

def test_stack_with_duplicate_elements():
    """Test that a stack with duplicate elements is not empty."""
    s = Stack(1, 1, 1)
    codeflash_output = s.empty() # 424ns -> 392ns (8.16% faster)

def test_stack_repr_and_empty():
    """Test that __repr__ does not affect empty()."""
    s = Stack()
    repr(s)
    codeflash_output = s.empty() # 447ns -> 417ns (7.19% faster)
    s.append(5)
    repr(s)
    codeflash_output = s.empty() # 233ns -> 197ns (18.3% faster)

def test_stack_len_consistency():
    """Test that len(s) == 0 iff s.empty() is True."""
    s = Stack()
    codeflash_output = s.empty() # 448ns -> 381ns (17.6% faster)
    s.append(1)
    codeflash_output = s.empty() # 226ns -> 199ns (13.6% faster)
    s.pop()
    codeflash_output = s.empty() # 148ns -> 145ns (2.07% faster)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.
#------------------------------------------------
from typing import List, TypeVar

# imports
import pytest  # used for our unit tests
from guardrails.classes.generic.stack import Stack

T = TypeVar("T")
from guardrails.classes.generic.stack import Stack

# unit tests

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

def test_empty_on_new_stack():
    """Test that a newly created stack is empty."""
    s = Stack()
    codeflash_output = s.empty() # 467ns -> 398ns (17.3% faster)

def test_empty_after_push():
    """Test that a stack with one item is not empty."""
    s = Stack()
    s.append(1)
    codeflash_output = s.empty() # 471ns -> 370ns (27.3% faster)

def test_empty_after_push_and_pop():
    """Test that a stack is empty after pushing and popping one item."""
    s = Stack()
    s.append("a")
    s.pop()
    codeflash_output = s.empty() # 500ns -> 387ns (29.2% faster)

def test_empty_with_multiple_elements():
    """Test that a stack with multiple elements is not empty."""
    s = Stack()
    for i in range(5):
        s.append(i)
    codeflash_output = s.empty() # 449ns -> 401ns (12.0% faster)

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

def test_empty_after_clear():
    """Test that a stack is empty after clearing."""
    s = Stack()
    for i in range(3):
        s.append(i)
    s.clear()
    codeflash_output = s.empty() # 480ns -> 399ns (20.3% faster)

def test_empty_after_pop_to_empty():
    """Test popping all elements one by one makes stack empty."""
    s = Stack()
    for i in range(3):
        s.append(i)
    s.pop()
    s.pop()
    s.pop()
    codeflash_output = s.empty() # 454ns -> 419ns (8.35% faster)

def test_empty_on_stack_with_none():
    """Test stack with None as an element is not empty."""
    s = Stack()
    s.append(None)
    codeflash_output = s.empty() # 458ns -> 394ns (16.2% faster)

def test_empty_on_stack_with_false():
    """Test stack with False as an element is not empty."""
    s = Stack()
    s.append(False)
    codeflash_output = s.empty() # 471ns -> 405ns (16.3% faster)

def test_empty_on_stack_with_empty_string():
    """Test stack with empty string as an element is not empty."""
    s = Stack()
    s.append("")
    codeflash_output = s.empty() # 458ns -> 406ns (12.8% faster)

def test_empty_on_stack_with_empty_list():
    """Test stack with empty list as an element is not empty."""
    s = Stack()
    s.append([])
    codeflash_output = s.empty() # 473ns -> 401ns (18.0% faster)

def test_empty_on_stack_with_zero():
    """Test stack with 0 as an element is not empty."""
    s = Stack()
    s.append(0)
    codeflash_output = s.empty() # 481ns -> 382ns (25.9% faster)

def test_empty_on_stack_with_multiple_data_types():
    """Test stack with mixed types is not empty."""
    s = Stack()
    s.append(1)
    s.append("a")
    s.append(None)
    s.append([])
    codeflash_output = s.empty() # 475ns -> 372ns (27.7% faster)

def test_empty_on_stack_initialized_with_args():
    """Test stack initialized with arguments is not empty."""
    s = Stack(1, 2, 3)
    codeflash_output = s.empty() # 466ns -> 389ns (19.8% faster)

def test_empty_on_stack_initialized_with_no_args():
    """Test stack initialized with no arguments is empty."""
    s = Stack()
    codeflash_output = s.empty() # 446ns -> 398ns (12.1% faster)

def test_empty_after_del_all_elements():
    """Test stack is empty after deleting all elements by index."""
    s = Stack()
    for i in range(4):
        s.append(i)
    del s[:]
    codeflash_output = s.empty() # 459ns -> 402ns (14.2% faster)

def test_empty_after_slice_assignment_to_empty():
    """Test stack is empty after slice assignment to empty list."""
    s = Stack()
    s.extend([1, 2, 3])
    s[:] = []
    codeflash_output = s.empty() # 450ns -> 389ns (15.7% faster)

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

def test_empty_large_stack_not_empty():
    """Test that a large stack is not empty."""
    s = Stack()
    s.extend(range(1000))
    codeflash_output = s.empty() # 518ns -> 393ns (31.8% faster)

def test_empty_large_stack_after_clear():
    """Test that a large stack is empty after being cleared."""
    s = Stack()
    s.extend(range(1000))
    s.clear()
    codeflash_output = s.empty() # 458ns -> 400ns (14.5% faster)

def test_empty_large_stack_pop_all():
    """Test that popping all elements from a large stack makes it empty."""
    s = Stack()
    s.extend(range(1000))
    for _ in range(1000):
        s.pop()
    codeflash_output = s.empty() # 436ns -> 397ns (9.82% faster)

def test_empty_large_stack_pop_some():
    """Test that popping some elements from a large stack does not make it empty."""
    s = Stack()
    s.extend(range(1000))
    for _ in range(500):
        s.pop()
    codeflash_output = s.empty() # 515ns -> 372ns (38.4% faster)

def test_empty_large_stack_with_various_types():
    """Test that a large stack with mixed types is not empty."""
    s = Stack()
    for i in range(500):
        s.append(i)
        s.append(str(i))
    codeflash_output = s.empty() # 515ns -> 358ns (43.9% faster)

# -------------------------------
# Additional Edge Cases
# -------------------------------

def test_empty_after_multiple_clear_and_push():
    """Test stack after multiple clear and push operations."""
    s = Stack()
    s.append(1)
    s.clear()
    codeflash_output = s.empty() # 470ns -> 410ns (14.6% faster)
    s.append(2)
    codeflash_output = s.empty() # 207ns -> 200ns (3.50% faster)
    s.clear()
    codeflash_output = s.empty() # 161ns -> 147ns (9.52% faster)

def test_empty_after_extend_and_remove_all():
    """Test stack after extend and removing all elements."""
    s = Stack()
    s.extend([1, 2, 3, 4])
    while s:
        s.pop()
    codeflash_output = s.empty() # 465ns -> 359ns (29.5% faster)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.

⏪ Replay Tests and Runtime

Test File::Test Function	Original ⏱️	Optimized ⏱️	Speedup
test_pytest_testsunit_teststest_guard_log_py_testsintegration_teststest_guard_py_testsunit_testsvalidator__replay_test_0.py::test_guardrails_classes_generic_stack_Stack_empty	66.6μs	56.5μs	17.9%✅

To edit these changes git checkout codeflash/optimize-Stack.empty-mh1rpa8o and push.