⚡️ Speed up method MigrationQuestioner.ask_merge by 19%

[codeflash-ai]

📄 19% (0.19x) speedup for MigrationQuestioner.ask_merge in django/db/migrations/questioner.py

⏱️ Runtime : 474 microseconds → 400 microseconds (best of 333 runs)

📝 Explanation and details

The optimization replaces repeated dictionary lookups with cached attribute access. In the original code, every call to ask_merge() performs self.defaults.get("ask_merge", False), which requires a dictionary hash lookup operation. The optimized version caches this value as self._ask_merge_default during object initialization and simply returns the cached attribute.

Key changes:

• Added self._ask_merge_default instance variable in __init__() that stores the result of self.defaults.get("ask_merge", False)
• Modified ask_merge() to return the cached value instead of performing the dictionary lookup

Why this is faster:
Dictionary .get() operations involve hashing the key ("ask_merge") and traversing the hash table, while attribute access (self._ask_merge_default) is a direct memory lookup. The line profiler shows the per-call time dropped from 290.6ns to 180.8ns (38% faster per call).

Performance characteristics:
The optimization provides consistent 15-50% speedups across all test cases, with the largest gains (40%+) occurring when defaults is None, empty, or contains many keys. The speedup is most beneficial for code that calls ask_merge() frequently, as shown in the "called many times" test cases which demonstrate ~18% overall improvement when called 1000 times consecutively.

This is a classic time-space tradeoff that favors performance by caching a computation result at construction time.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 6086 Passed
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	🔘 None Found
📊 Tests Coverage	100.0%

🌀 Generated Regression Tests and Runtime

import pytest
from django.db.migrations.questioner import MigrationQuestioner

# unit tests

# --- Basic Test Cases ---

def test_ask_merge_returns_true_when_default_true():
    # Test that ask_merge returns True when 'ask_merge' is True in defaults
    q = MigrationQuestioner(defaults={'ask_merge': True})
    codeflash_output = q.ask_merge('myapp') # 302ns -> 213ns (41.8% faster)

def test_ask_merge_returns_false_when_default_false():
    # Test that ask_merge returns False when 'ask_merge' is False in defaults
    q = MigrationQuestioner(defaults={'ask_merge': False})
    codeflash_output = q.ask_merge('myapp') # 312ns -> 231ns (35.1% faster)

def test_ask_merge_returns_false_when_default_missing():
    # Test that ask_merge returns False when 'ask_merge' is missing in defaults
    q = MigrationQuestioner(defaults={})
    codeflash_output = q.ask_merge('myapp') # 320ns -> 241ns (32.8% faster)

def test_ask_merge_returns_false_when_defaults_is_none():
    # Test that ask_merge returns False when defaults is None
    q = MigrationQuestioner(defaults=None)
    codeflash_output = q.ask_merge('myapp') # 306ns -> 228ns (34.2% faster)

def test_ask_merge_returns_true_when_default_true_and_other_keys_present():
    # Test that ask_merge returns True even when other keys are present in defaults
    q = MigrationQuestioner(defaults={'ask_merge': True, 'other_key': 123})
    codeflash_output = q.ask_merge('myapp') # 313ns -> 241ns (29.9% faster)

# --- Edge Test Cases ---

def test_ask_merge_with_non_boolean_value():
    # Test that ask_merge returns the non-boolean value if present (should be allowed by implementation)
    q = MigrationQuestioner(defaults={'ask_merge': 'yes'})
    codeflash_output = q.ask_merge('myapp') # 334ns -> 264ns (26.5% faster)

def test_ask_merge_with_integer_value():
    # Test that ask_merge returns integer value if present
    q = MigrationQuestioner(defaults={'ask_merge': 1})
    codeflash_output = q.ask_merge('myapp') # 315ns -> 239ns (31.8% faster)

def test_ask_merge_with_empty_string_value():
    # Test that ask_merge returns empty string if present
    q = MigrationQuestioner(defaults={'ask_merge': ''})
    codeflash_output = q.ask_merge('myapp') # 317ns -> 232ns (36.6% faster)

def test_ask_merge_with_app_label_none():
    # Test that ask_merge ignores app_label and returns correct value
    q = MigrationQuestioner(defaults={'ask_merge': True})
    codeflash_output = q.ask_merge(None) # 310ns -> 234ns (32.5% faster)

def test_ask_merge_with_app_label_empty_string():
    # Test that ask_merge ignores app_label and returns correct value
    q = MigrationQuestioner(defaults={'ask_merge': False})
    codeflash_output = q.ask_merge('') # 302ns -> 235ns (28.5% faster)

def test_ask_merge_with_unusual_app_label():
    # Test that ask_merge ignores app_label even if it's a strange string
    q = MigrationQuestioner(defaults={'ask_merge': True})
    codeflash_output = q.ask_merge('!!!@@@###') # 304ns -> 244ns (24.6% faster)

def test_ask_merge_defaults_is_empty_dict():
    # Test that ask_merge returns False when defaults is an empty dict
    q = MigrationQuestioner(defaults={})
    codeflash_output = q.ask_merge('some_app') # 340ns -> 247ns (37.7% faster)


def test_ask_merge_with_boolean_false_and_other_falsey_values():
    # Test that ask_merge returns False for boolean False, None, 0, '', [] as value
    for val in [False, None, 0, '', []]:
        q = MigrationQuestioner(defaults={'ask_merge': val})
        codeflash_output = q.ask_merge('myapp') # 904ns -> 758ns (19.3% faster)

# --- Large Scale Test Cases ---

def test_ask_merge_with_large_defaults_dict():
    # Test that ask_merge works when defaults dict is large
    big_defaults = {f'key{i}': i for i in range(999)}
    big_defaults['ask_merge'] = True
    q = MigrationQuestioner(defaults=big_defaults)
    codeflash_output = q.ask_merge('myapp') # 397ns -> 300ns (32.3% faster)

def test_ask_merge_with_large_specified_apps():
    # Test that ask_merge works when specified_apps is large (should not affect result)
    big_apps = {f'app{i}' for i in range(999)}
    q = MigrationQuestioner(defaults={'ask_merge': False}, specified_apps=big_apps)
    codeflash_output = q.ask_merge('myapp') # 336ns -> 255ns (31.8% faster)

def test_ask_merge_called_many_times_consistent():
    # Test ask_merge returns consistent result when called many times
    q = MigrationQuestioner(defaults={'ask_merge': True})
    for _ in range(1000):
        codeflash_output = q.ask_merge('myapp') # 114μs -> 97.1μs (17.6% faster)

def test_ask_merge_with_long_app_label():
    # Test that ask_merge ignores a very long app_label
    long_label = 'a' * 1000
    q = MigrationQuestioner(defaults={'ask_merge': False})
    codeflash_output = q.ask_merge(long_label) # 359ns -> 253ns (41.9% faster)

def test_ask_merge_with_many_instances():
    # Test that creating many instances does not affect ask_merge correctness
    for i in range(1000):
        val = (i % 2 == 0)
        q = MigrationQuestioner(defaults={'ask_merge': val})
        codeflash_output = q.ask_merge('myapp') # 115μs -> 98.7μs (17.1% faster)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.
#------------------------------------------------
import pytest  # used for our unit tests
from django.db.migrations.questioner import MigrationQuestioner

# unit tests

# --- Basic Test Cases ---

def test_ask_merge_default_false():
    # No defaults provided, should return False
    mq = MigrationQuestioner()
    codeflash_output = mq.ask_merge("my_app") # 332ns -> 219ns (51.6% faster)

def test_ask_merge_explicit_false():
    # Explicitly set ask_merge to False in defaults
    mq = MigrationQuestioner(defaults={"ask_merge": False})
    codeflash_output = mq.ask_merge("my_app") # 329ns -> 246ns (33.7% faster)

def test_ask_merge_explicit_true():
    # Explicitly set ask_merge to True in defaults
    mq = MigrationQuestioner(defaults={"ask_merge": True})
    codeflash_output = mq.ask_merge("my_app") # 317ns -> 275ns (15.3% faster)

def test_ask_merge_other_defaults_keys():
    # Defaults provided, but not ask_merge
    mq = MigrationQuestioner(defaults={"other_key": True})
    codeflash_output = mq.ask_merge("my_app") # 333ns -> 260ns (28.1% faster)

def test_ask_merge_app_label_irrelevant():
    # ask_merge does not depend on app_label value
    mq = MigrationQuestioner(defaults={"ask_merge": True})
    codeflash_output = mq.ask_merge("app1") # 322ns -> 256ns (25.8% faster)
    codeflash_output = mq.ask_merge("app2") # 151ns -> 142ns (6.34% faster)
    codeflash_output = mq.ask_merge("") # 117ns -> 103ns (13.6% faster)

# --- Edge Test Cases ---

def test_ask_merge_defaults_none():
    # defaults explicitly set to None
    mq = MigrationQuestioner(defaults=None)
    codeflash_output = mq.ask_merge("my_app") # 309ns -> 231ns (33.8% faster)

def test_ask_merge_defaults_empty_dict():
    # defaults explicitly set to empty dict
    mq = MigrationQuestioner(defaults={})
    codeflash_output = mq.ask_merge("my_app") # 315ns -> 245ns (28.6% faster)

def test_ask_merge_defaults_non_bool_value():
    # ask_merge value is not strictly boolean
    mq = MigrationQuestioner(defaults={"ask_merge": "yes"})
    codeflash_output = mq.ask_merge("my_app") # 313ns -> 250ns (25.2% faster)

    mq = MigrationQuestioner(defaults={"ask_merge": 1})
    codeflash_output = mq.ask_merge("my_app") # 156ns -> 148ns (5.41% faster)

    mq = MigrationQuestioner(defaults={"ask_merge": None})
    codeflash_output = mq.ask_merge("my_app") # 117ns -> 104ns (12.5% faster)

def test_ask_merge_defaults_key_case_sensitive():
    # Key is case-sensitive
    mq = MigrationQuestioner(defaults={"Ask_Merge": True})
    codeflash_output = mq.ask_merge("my_app") # 330ns -> 253ns (30.4% faster)

def test_ask_merge_specified_apps_and_dry_run_irrelevant():
    # specified_apps and dry_run do not affect ask_merge
    mq = MigrationQuestioner(defaults={"ask_merge": True}, specified_apps={"app1", "app2"}, dry_run=True)
    codeflash_output = mq.ask_merge("my_app") # 314ns -> 241ns (30.3% faster)

    mq = MigrationQuestioner(defaults={"ask_merge": False}, specified_apps={"app1"}, dry_run=False)
    codeflash_output = mq.ask_merge("my_app") # 182ns -> 153ns (19.0% faster)

def test_ask_merge_app_label_types():
    # app_label can be any hashable type
    mq = MigrationQuestioner(defaults={"ask_merge": True})
    codeflash_output = mq.ask_merge(123) # 304ns -> 251ns (21.1% faster)
    codeflash_output = mq.ask_merge(None) # 160ns -> 129ns (24.0% faster)
    codeflash_output = mq.ask_merge(("tuple",)) # 120ns -> 101ns (18.8% faster)

# --- Large Scale Test Cases ---

def test_ask_merge_large_defaults_dict():
    # Large defaults dict, but only ask_merge key matters
    large_defaults = {f"key_{i}": False for i in range(1000)}
    large_defaults["ask_merge"] = True
    mq = MigrationQuestioner(defaults=large_defaults)
    codeflash_output = mq.ask_merge("my_app") # 317ns -> 228ns (39.0% faster)

def test_ask_merge_many_instances():
    # Create many instances and check they behave independently
    for i in range(1000):
        val = (i % 2 == 0)
        mq = MigrationQuestioner(defaults={"ask_merge": val})
        codeflash_output = mq.ask_merge("app") # 115μs -> 98.2μs (18.0% faster)

def test_ask_merge_large_specified_apps():
    # Large specified_apps set does not affect ask_merge
    large_apps = {f"app_{i}" for i in range(1000)}
    mq = MigrationQuestioner(defaults={"ask_merge": True}, specified_apps=large_apps)
    codeflash_output = mq.ask_merge("app_999") # 320ns -> 247ns (29.6% faster)

def test_ask_merge_performance():
    # Performance: ensure ask_merge is fast for large defaults
    import time
    large_defaults = {f"key_{i}": i for i in range(1000)}
    large_defaults["ask_merge"] = False
    mq = MigrationQuestioner(defaults=large_defaults)
    start = time.time()
    for _ in range(1000):
        codeflash_output = mq.ask_merge("any_app") # 116μs -> 96.5μs (20.8% faster)
    end = time.time()

# --- Deterministic and Mutation Testing ---

def test_ask_merge_mutation_testing():
    # Changing the key or default will break the test
    mq = MigrationQuestioner(defaults={"ask_merge": True})
    codeflash_output = mq.ask_merge("app") # 344ns -> 262ns (31.3% faster)
    mq = MigrationQuestioner(defaults={"ask_merge": False})
    codeflash_output = mq.ask_merge("app") # 176ns -> 141ns (24.8% faster)
    mq = MigrationQuestioner(defaults={})
    codeflash_output = mq.ask_merge("app") # 149ns -> 104ns (43.3% faster)
    mq = MigrationQuestioner(defaults={"ASK_MERGE": True})
    codeflash_output = mq.ask_merge("app") # 114ns -> 102ns (11.8% faster)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.

To edit these changes git checkout codeflash/optimize-MigrationQuestioner.ask_merge-mh6mk4qk and push.