Swap onum and lnum features in SFNT file. Written for Robin Mientjes

swapFigs.py

import os
from fontTools.ttLib import TTFont
    
    
'''
list of SFNTs
'''
fontList = []

for path in fontList:

    ext = os.path.splitext(path)[1]
    savePath = path.replace(ext,f"-swapped{ext}")

    f = TTFont(path)

    GSUB = f["GSUB"]

    lnum = []
    onum = []

    for r in GSUB.table.FeatureList.FeatureRecord:
        if r.FeatureTag == "lnum":
            lnum.append(r.Feature.LookupListIndex[0])
            
    for r in GSUB.table.FeatureList.FeatureRecord:
        if r.FeatureTag == "onum":
            onum.append(r.Feature.LookupListIndex[0])

    lnum  = sorted(list(set(lnum)))
    onum  = sorted(list(set(onum)))
    
    lnumMapping = None
    onumMapping = None
    lnumSubtable = None
    onumSubtable = None
    
    if lnum and onum:
        for LookupID in lnum:
            lnumLookup = GSUB.table.LookupList.Lookup[LookupID]
            for Subtable in lnumLookup.SubTable:
                if Subtable.LookupType == 1:
                    lnumSubtable = Subtable
                    lnumMapping = Subtable.mapping
                else:
                    print("lnum lookup isn't type1")
        for LookupID in onum:
            onumLookup = GSUB.table.LookupList.Lookup[LookupID]
            for Subtable in onumLookup.SubTable:
                if Subtable.LookupType == 1:
                    onumSubtable = Subtable
                    onumMapping = Subtable.mapping
                else:
                    print("onum lookup isn't type1")
                    
            if onumMapping and lnumMapping:
                onumSubtable.mapping = lnumMapping
                lnumSubtable.mapping = onumMapping
                
                f.save(savePath)