lookup-size.py

from fontTools.ttLib import TTFont
from fontTools.ttLib.tables.otBase import OTTableWriter
import sys
from fontTools.feaLib.lookupDebugInfo import LOOKUP_DEBUG_INFO_KEY

font = TTFont(sys.argv[1])

def locate(table, ix):
	if "Debg" not in font:
		return str(ix)
	debg = font["Debg"].data[LOOKUP_DEBUG_INFO_KEY][table].get(str(ix))
	if debg:
		return f"{ix} = {debg[0]} ({debg[1]})"
	return str(ix)

for table in ["GSUB", "GPOS"]:
	print(f"{table} table")
	print("==========\n")
	lookups = font.get(table).table.LookupList.Lookup
	sizes = []
	for ix, lookup in enumerate(lookups):
		writer = OTTableWriter()
		lookup.compile(writer, font)
		sizes.append((locate(table, ix), len(writer.getAllData())))

	for location, size in (list(sorted(sizes, key=lambda a:-a[1])))[0:10]:
		print(location, "\t", size)