RoboFont script to find unexpected kerning exceptions in a UFO, then remove those kerns and replace them with kerns using groups.

find-n-fix-unintended-kerning-exceptions.py

"""
    Find kerning exceptions in a UFO, then remove those kerns and replace them with kerns using groups.
    
    Why?
    Sometimes, if you add kerning to a font early, you can wind up with unexpected kerning exceptions
    when you add new characters to the font. E.g. ('G', 'asterisk') makes sense until you add 'Gbreve'.

    USAGE: 
    Configure side1_ignore & side2_ignore lists below, then run this script in RoboFont.
    - It won’t autosave your UFOs, because you should probably review the results before saving. 
    - Better yet, you should use Git to version your files, so you can see exactly what changes 
      before sticking with these batch edits.
      
    DISCLAIMER: 
    This code is messy and written to solve an immediate problem for a few UFOs. It could be further improved.
"""

from vanilla.dialogs import *
from mojo.UI import OutputWindow


# ---------------------------------------------

# glyph names to ignore on side 1 and side 2 of kerns (e.g. because T.ultra has intentional exceptions)
side1_ignore = "T T.ultra tcaron".split(" ")
side2_ignore = "T T.ultra Oslash".split(" ")

# ---------------------------------------------

# prompt user to open UFOs in RoboFont
files =  getFile("Select files to edit",
    allowsMultipleSelection=True, fileTypes=["ufo"])

OutputWindow().clear()

output = ""

for filepath in files:
    font = OpenFont(filepath)
    output += "\n"
    output += "✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨\n"
    output += "✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨\n"
    output += "✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨\n"
    output += "\n"
    output += f"{font.info.familyName} {font.info.styleName}\n"

    double_exceptions = []
    side1_exceptions = []
    side2_exceptions = []

    for kern in font.kerning:

        if "kern1" not in kern[0] and "kern2" not in kern[1]:
            if "kern1" in " ".join(font.groups.findGlyph(kern[0])) and "kern2" in " ".join(font.groups.findGlyph(kern[1])):
                double_exceptions.append(kern)

                # move on to next kern to avoid putting into side1 / side2 lists
                continue

        # if side 1 is not a group
        if "kern1" not in kern[0]:
            # check if it is in a side 1 group
            if "kern1" in " ".join(font.groups.findGlyph(kern[0])):
                side1_exceptions.append(kern)

        # if side 2 is not a group
        if "kern2" not in kern[1]:
            # check if it is in a side 2 group
            if "kern2" in " ".join(font.groups.findGlyph(kern[1])):
                side2_exceptions.append(kern)

    ## uncomment to see just lists of kerns with exceptions
    # output += "\n\nℹ️ SIDE 1+2 EXCEPTIONS\n"
    # output += "\n".join([" ".join(list(kern)) for kern in double_exceptions]) + "\n"
    # output += "\n\nℹ️ SIDE 1 EXCEPTIONS\n"
    # output += "\n".join([" ".join(list(kern)) for kern in side1_exceptions]) + "\n"
    # output += "\n\nℹ️ SIDE 2 EXCEPTIONS\n"
    # output += "\n".join([" ".join(list(kern)) for kern in side2_exceptions]) + "\n"

    output += "\n"
    output += "\n"
    output += "----------------------------------------------------------------------------\n"
    output += "SIDE 1 + 2 EXCEPTIONS REMOVED\n"
    output += "\n"

    for pair in double_exceptions:

        # if side not in "ignore" list
        if pair[0] not in side1_ignore and pair[1] not in side2_ignore:

            # get kern value and remove pair
            value = font.kerning.pop(pair)

            # make kern with the group instead
            newPair = tuple([font.groups.findGlyph(pair[0])[0], font.groups.findGlyph(pair[1])[-1]])
            font.kerning[newPair] = value
            oldPair, newPair = " | ".join(list(pair)), " | ".join(list(newPair))
            output += f"{oldPair.rjust(40)}   →   {newPair.ljust(50,' ')}: {value}\n\n"

    output += "\n"
    output += "\n"
    output += "----------------------------------------------------------------------------\n"
    output += "SIDE 1 EXCEPTIONS REMOVED\n"
    output += "\n"

    for pair in side1_exceptions:

        # if side not in "ignore" list
        if pair[0] not in side1_ignore and pair[1] not in side2_ignore:

            # get kern value and remove pair
            value = font.kerning.pop(pair)

            # make kern with the group instead
            newPair = tuple([font.groups.findGlyph(pair[0])[0], pair[1]])
            font.kerning[newPair] = value
            oldPair, newPair = " | ".join(list(pair)), " | ".join(list(newPair))
            output += f"{oldPair.rjust(40)}   →   {newPair.ljust(50,' ')}: {value}\n\n"
    
    output += "\n"
    output += "\n"
    output += "----------------------------------------------------------------------------\n"
    output += "SIDE 2 EXCEPTIONS REMOVED\n"
    output += "\n"

    for pair in side2_exceptions:

        # if side not in "ignore" list
        if pair[0] not in side1_ignore and pair[1] not in side2_ignore:

            # get kern value and remove pair
            value = font.kerning.pop(pair)

            # make kern with the group instead
            newPair = tuple([pair[0], font.groups.findGlyph(pair[1])[-1]])
            font.kerning[newPair] = value
            oldPair, newPair = " | ".join(list(pair)), " | ".join(list(newPair))
            output += f"{oldPair.rjust(40)}   →   {newPair.ljust(50)}: {value}\n\n"

    ## uncomment to automatically save and close, but only do this if you are confident in the results
    # font.save()
    # font.close()

print(output)

OutputWindow().show()

This will output text to show what has changed, like:

✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨
✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨
✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨✨

Name Sans Text Ultra

----------------------------------------------------------------------------
SIDE 1 + 2 EXCEPTIONS REMOVED

                              L | hyphen   →   public.kern1.L | public.kern2.hyphen              : 0

                                   L | l   →   public.kern1.L | public.kern2.l               : -20

                                   L | t   →   public.kern1.L | public.kern2.t                   : -70

[etc]

----------------------------------------------------------------------------
SIDE 1 EXCEPTIONS REMOVED

                            G | asterisk   →   public.kern1.G | asterisk                         : -30

                           G | backslash   →   public.kern1.G | backslash                        : -95

                             G | percent   →   public.kern1.G | percent                          : -20

[etc]

----------------------------------------------------------------------------
SIDE 2 EXCEPTIONS REMOVED

                                   F | p   →   F | public.kern2.n                                : -10

                                   F | s   →   F | public.kern2.s                                : -105

                                   F | t   →   F | public.kern2.t                                : -10

[etc]