gh-145131: difflib.Differ._fancy_replace performance (re-use ratio)

[dg-pb]

• Issue: difflib.Differ._fancy_replace performance (re-use ratio) #145131

[tim-one]

I'll merge it, but reluctantly. It damages readability a little for very little gain. The matching blocks were already computed and cached for reuse on the first call to cr(), so it saves very little time.- just saves summing the lengths of the already-computed matching blocks between two lines. Why bother? It's not worth it to me, but damages readability so little I won't argue about it. So, thanks - I guess 😉.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Ubuntu Shared 3.x (tier-1) has failed when building commit 79f6caf.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/506/builds/12404) and take a look at the build logs.
4. Check if the failure is related to this commit (79f6caf) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/506/builds/12404

Failed tests:

• test_pyrepl

Failed subtests:

• test_repl_eio - test.test_pyrepl.test_unix_console.TestUnixConsoleEIOHandling.test_repl_eio

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/subprocess.py", line 1191, in __del__
    _warn("subprocess %s is still running" % self.pid,
    ~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
          ResourceWarning, source=self)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ResourceWarning: subprocess 1078638 is still running
Warning -- Unraisable exception
Exception ignored while finalizing file <_io.FileIO name=10 mode='rb' closefd=True>:
Traceback (most recent call last):
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/unittest/case.py", line 666, in run
    with outcome.testPartExecutor(self):
         ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
ResourceWarning: unclosed file <_io.TextIOWrapper name=10 encoding='utf-8'>
Warning -- Unraisable exception
Exception ignored while finalizing file <_io.FileIO name=8 mode='rb' closefd=True>:
Traceback (most recent call last):
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/unittest/case.py", line 666, in run
    with outcome.testPartExecutor(self):
         ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
ResourceWarning: unclosed file <_io.TextIOWrapper name=8 encoding='utf-8'>


Traceback (most recent call last):
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/subprocess.py", line 1191, in __del__
    _warn("subprocess %s is still running" % self.pid,
    ~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
          ResourceWarning, source=self)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ResourceWarning: subprocess 1109411 is still running
Warning -- Unraisable exception
Exception ignored while finalizing file <_io.FileIO name=10 mode='rb' closefd=True>:
Traceback (most recent call last):
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/unittest/case.py", line 666, in run
    with outcome.testPartExecutor(self):
         ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
ResourceWarning: unclosed file <_io.TextIOWrapper name=10 encoding='utf-8'>
Warning -- Unraisable exception
Exception ignored while finalizing file <_io.FileIO name=8 mode='rb' closefd=True>:
Traceback (most recent call last):
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/unittest/case.py", line 666, in run
    with outcome.testPartExecutor(self):
         ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
ResourceWarning: unclosed file <_io.TextIOWrapper name=8 encoding='utf-8'>


Traceback (most recent call last):
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/test_pyrepl/test_unix_console.py", line 390, in test_repl_eio
    _, err = proc.communicate(timeout=support.LONG_TIMEOUT)
             ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/subprocess.py", line 1273, in communicate
    stdout, stderr = self._communicate(input, endtime, timeout)
                     ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/subprocess.py", line 2293, in _communicate
    self._check_timeout(endtime, orig_timeout, stdout, stderr)
    ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/subprocess.py", line 1320, in _check_timeout
    raise TimeoutExpired(
    ...<2 lines>...
            stderr=b''.join(stderr_seq) if stderr_seq else None)
subprocess.TimeoutExpired: Command '['/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/python', '-E', '-S', '/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/test_pyrepl/eio_test_script.py']' timed out after 300.0 seconds