# remove -M arg if user supplies 'no_renames' or 'M' kwargs 
        if not any(x in kwargs for x in ('no_renames','M')):
            args.append("-M")  # check for renames, in both formats
        
        # manually convert '-M'
        if 'M' in kwargs:
            args.append(f"-M{str(kwargs['M'])}")
            del(kwargs['M'])
            

commitA.diff(commitB, M='75%')
produces:
git diff-tree 58259d006066372eb337cce81caf97365eb30f1e 22315b3c433865970e0a2fcd1b599786c2e01703 -r --abbrev=40 --full-index -M75% --raw -z --no-color

commitA.diff(commitB, no_renames=True)
produces:
git diff-tree --no-renames 58259d006066372eb337cce81caf97365eb30f1e 22315b3c433865970e0a2fcd1b599786c2e01703 -r --abbrev=40 --full-index --raw -z --no-color

default behavior stays the same
commitA.diff(commitB)
produces:
git diff-tree 58259d006066372eb337cce81caf97365eb30f1e 22315b3c433865970e0a2fcd1b599786c2e01703 -r --abbrev=40 --full-index -M --raw -z --no-color

Maybe that could be generalized (and tested) to become a contribution - it looks like a genuine improvement without adding too much complexity.

Hey Bryon,

So I took another look into the command line formatting issue. It turns out there is an option to format those single char kawrgs.
split_single_char_options controls the inclusion of a space character when constructing the git command line.

original:
commitA.diff(commitB, M='75%')

produces the -M 75%: (space included)
git diff-tree -M 75% 69a8e0b10c8695d7f073c3b32c647aa8e892b1e2 140ef4c33fa5a899cd8d1dfb15a03c342a49a95c -r --abbrev=40 --full-index --raw -z --no-color

Including option to format single char kwargs:
commitA.diff(commitB, split_single_char_options=False ,M='75%')
produces the -M75% (space removed)
git diff-tree -M75% 69a8e0b10c8695d7f073c3b32c647aa8e892b1e2 140ef4c33fa5a899cd8d1dfb15a03c342a49a95c -r --abbrev=40 --full-index --raw -z --no-color

So it looks like all we need is to remove the default -M when the user wants to override it with either --find-renames= or -M or --no-renames

    # remove default '-M' arg (check for renames) if user is overriding it
    if not any(x in kwargs for x in ('find_renames', 'no_renames','M')):
        args.append("-M")

The remaining kwargs can be processed through the normal routines.

It may also be worth adding the split_single_char_options option in the docs.

I see, thanks so much for investigating this. A PR to improve the situation would definitely be welcome. Thank you.

Hey nwcm! The PR was finished last week. You can probably download the source now, or wait for the official 3.1.31 release.
#1551
Usage examples can be found in test/test_diff.py test_rename_override().