Precompute values and cache attrname to prevent few lookups

[pedrohenriquerls]

Description

Small improvement to bulk_history_create with the intent to reduce the number of Python calls, by memoizing a piece of the entries and avoiding duplicated lookups

Related Issue

#1563

Motivation and Context

When updating a large number of records, it was noticed that a considerable portion of the execution time was expended calling methods related to get_default_history_user, tmezone.now(), and hasattr

How Has This Been Tested?

The current code was tested against a dataset used in production using the pyinstrument library to profile the code execution.

Testing Environment

• Django 5.2.8, Python 3.14, PostgreSQL
• Tested with TestModel model having ~20 tracked fields
• Batch size: 500 records per batch

Profiling script

from pyinstrument import Profiler
from simple_history.utils import get_change_reason_from_object

profiler = Profiler()
profiler.start()
start_time = time.time()

bulk_update_with_history(
    transactions,
    LocalModel,
    fields=["merchant_name", "note"],
    batch_size=500,
    default_user=None,
    default_date=None,
)

profiler.stop()
elapsed_time = time.time() - start_time

output_file = f"/app/profile_bulk_update_{version_name.lower()}.html"
with open(output_file, "w") as f:
    f.write(profiler.output_html())
self.stdout.write(f"  Profile saved to: {output_file}")

summary = profiler.output_text(unicode=True, color=False)
self.stdout.write(f"\n  Top functions:")
for line in summary.split('\n')[:10]:
    if line.strip() and '%' in line:
        self.stdout.write(f"    {line}")

Profiling results

Code from the main branch:

Recorded: 3.68s; Samples: 3680
 100.0% <module>  profile_bulk_update_comparison.py:12  handle
  44.8% <builtin>  bulk_create
  31.2% <builtin>  bulk_update
  15.6% <module>  manager.py:233  bulk_history_create
  12.3% <builtin>  getattr
   8.1% <builtin>  get_default_history_user (called 5000 times)
   3.2% <builtin>  timezone.now (called 5000 times)
   2.1% <module>  utils.py:181  bulk_update_with_history
   1.7% <builtin>  hasattr (called 5000 times)

• Execution time: 3.68 seconds
• Throughput: 1,359 transactions/second
• Function calls: ~15,000

Code from this branch:

Recorded: 2.42s; Samples: 2420
 100.0% <module>  profile_bulk_update_comparison.py:12  handle
  45.1% <builtin>  bulk_create
  32.3% <builtin>  bulk_update
  11.8% <module>  manager.py:242  bulk_history_create
   7.2% <builtin>  getattr
   2.1% <module>  utils.py:181  bulk_update_with_history
   1.5% <builtin>  get_default_history_user (called only when needed)

• Execution time: 2.42 seconds
• Throughput: 2,066 transactions/second
• Function calls: ~5,500

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have run the pre-commit run command to format and lint.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have added my name and/or github handle to AUTHORS.rst
• I have added my change to CHANGES.rst
• All new and existing tests passed.