gh-118150: difflib: expose autojunk flag from SequenceMatcher to public methods and functions

[faithlesstomas]

Until now difflib methods and functions took SequenceMatcher class kwarg autojunk by default which is set up to be True in this class.. This PR aims to expose this flag to the public methods and functions of this module, in order that user can choose behavior of this option in SequenceMatcher.

Issue: #118150
Related PR: #153892

• Issue: Difflib creates unreasonably large diffs #118150

[python-cla-bot]

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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[faithlesstomas]

Quick check if this works for the original issue test:

 #!/usr/bin/python3                                                                                                                                                          
                                                                                                                                                                              
  import difflib                                                                                                                                                              
                                                                                                                                                                              
  def get_lines(filename):                                                                                                                                                    
      with open(filename, 'r', encoding='utf8') as fd:                                                                                                                        
          return fd.readlines()                                                                                                                                               
                                                                                                                                                                              
  for autojunk in (True, False):                                                                                                                                              
                                                                                                                                                                              
      old_new = list(difflib.unified_diff(                                                                                                                                    
          get_lines('small.external.old.json'),                                                                                                                               
          get_lines('small.external.new.json'),                                                                                                                               
          autojunk=autojunk                                                                                                                                                   
      ))                                                                                                                                                                      
      new_old = list(difflib.unified_diff(                                                                                                                                    
          get_lines('small.external.new.json'),                                                                                                                               
          get_lines('small.external.old.json'),                                                                                                                               
          autojunk=autojunk                                                                                                                                                   
      ))                                                                                                                                                                      
                                                                                                                                                                              
      print('Autojunk flag:', autojunk)                                                                                                                                       
      print('diff external.old external.new.json | wc -l')                                                                                                                    
      print(len(old_new))                                                                                                                                                     
      print('diff external.new external.old.json | wc -l')                                                                                                                    
      print(len(new_old))                                                                                                                                                     

Autojunk flag: True
diff external.old external.new.json | wc -l
90
diff -u external.new external.old.json | wc -l
25
Autojunk flag: False
diff external.old external.new.json | wc -l
25
diff -u external.new external.old.json | wc -l
25

#118150 (comment)

[Lenormju]

I think the Documentation (Doc/library/difflib.rst) should get updated too to include this new parameter.

[Lenormju]

@faithlesstomas you should review this file, it seems to have been very badly AI-generated.

[faithlesstomas]

@Lenormju I wouldn't have thought that my bad English could be considered to be AI generated :) Do you have any specific suggestion what should be improved in this description?

BTW, nothing in this PR was AI generated.

[Lenormju]

@faithlesstomas The commit was titled difflib - fix NEWS issue with ref. not found which I found strange that a human would commit "ref. not found". Also the NEWS file contain these comments :

# # Uncomment one of these "section:" lines to specify which section # this
entry should go in in Misc/NEWS.d. # #.. section: Security #.. section: Core
and Builtins #.. section: Library #.. section: Documentation #.. section:
Tests #.. section: Build #.. section: Windows #.. section: macOS #..
section: IDLE #.. section: Tools/Demos #.. section: C API

# Write your Misc/NEWS.d entry below.  It should be a simple ReST paragraph.
# Don't start with "- Issue #<n>: " or "- gh-issue-<n>: " or that sort of
stuff.
###########################################################################

Which look like a template you did not erase.

I was not basing myself on the English, instead on all the rest. But if it wasn't, sorry.

[faithlesstomas]

@Lenormju Sorry, that was my mistake - I thought this comment is to be left there. Also I didn't know how properly reference a class in ReST... But besides that, does this PR look good now?