build.py

import fontforge
import sys
import unicodedata

FLAGS = ("opentype", "omit-instructions", "no-mac-names")  # , 'short-post')

font = fontforge.open(sys.argv[1])

font.selection.all()
font.correctReferences()
font.selection.none()

allA = set()
for glyph in font.glyphs():
    if glyph.unicode > 0:
        ct = unicodedata.category(chr(glyph.unicode))
        if ct[0] not in {"L", "M", "N"}:
            continue
    allA.add(glyph.glyphname)

allE = allA - {
    "uni0627",
    "uni0622",
    "uni0671",
    "uni0627.fina",
    "uni0671.fina",
    "uni0648",
}
with open(sys.argv[3]) as f:
    classes = f"""
@All = [{' '.join(sorted(allA))}];
@AllExceptWawAndAlef = [{' '.join(sorted(allE))}];
"""
    fea = f.read().replace("%CLASSES%", classes)

with open(sys.argv[1].replace(".sfd", ".fea"), "w") as f:
    f.write(fea)

font.mergeFeature(f.name)

font.generate(sys.argv[2], flags=FLAGS)