A robofont script that filters through a folder of font masters for minimum and maximum grade(labelled "MinGrade" and "MaxGrade" but that can get variable-assigned), and does the math and matching to equate the glyph widths (this assumes equal advance weights and only addresses potential spacing problems)

matchWidths.py

def makePairs(path, stylename, maxVal, minVal):
    separatemasters(path, maxVal, minVal)
    listName = []
    for f in maxFonts:
        if stylename in f:
            listName.append(f)
            for m in minFonts:
                if stylename in m:
                    listName.append(m)
            return(list(dict.fromkeys(listName))) #list(dict.fromkeys(x)) is a good way to get a list with stripped duplicates

def matchWidths(folderPath):
    for style in baseStyles:
        thisPair = (makePairs(folderPath, style, "MaxGrade", "MinGrade"))
        maxMaster = OpenFont(thisPair[0], showInterface = False)
        minMaster = OpenFont(thisPair[1], showInterface = False)
        for glyphName in maxMaster.keys():
            if maxMaster[glyphName]:
                maxMaster[glyphName].leftMargin=int(maxMaster[glyphName].leftMargin)
                maxMaster[glyphName].rightMargin=int(maxMaster[glyphName].rightMargin)
                widthDiff=maxMaster[glyphName].width-minMaster[glyphName].width
                minMaster[glyphName].leftMargin+=int(widthDiff/2)
                minMaster[glyphName].rightMargin+=int(widthDiff/2)
                if minMaster[glyphName].width > maxMaster[glyphName].width:
                     minMaster[glyphName].rightMargin += -1
                if maxMaster[glyphName].width > minMaster[glyphName].width:
                     maxMaster[glyphName].rightMargin += -1
        maxMaster.save(folderPath + maxMaster.info.familyName + " " + maxMaster.info.styleName + ".ufo")
        minMaster.save(folderPath + minMaster.info.familyName + " " + minMaster.info.styleName + ".ufo")
            # print(f"Min Master ---> left margin: {minMaster[glyph].leftMargin} | right margin: {minMaster[glyph].rightMargin} | width: {minMaster[glyph].width}")
            # print(f"Max Master ---> left margin: {maxMaster[glyph].leftMargin} | right margin: {maxMaster[glyph].rightMargin} | width: {maxMaster[glyph].width}")
            
matchWidths("folder path/")