import re
s = 'AB+B+" HELLO"+TODAY()/C* 100'
rs = re.sub(r'"[^"]*"|\bTODAY\b|\b([A-Z]+)\b',
lambda m: 'a2num("' + m.group(1) + '")' if m.group(1) else m.group(), s)
print (rs)
aW1wb3J0IHJlCgpzID0gJ0FCK0IrIiBIRUxMTyIrVE9EQVkoKS9DKiAxMDAnCnJzID0gcmUuc3ViKHInIlteIl0qInxcYlRPREFZXGJ8XGIoW0EtWl0rKVxiJywKICAgICBsYW1iZGEgbTogJ2EybnVtKCInICsgbS5ncm91cCgxKSArICciKScgaWYgbS5ncm91cCgxKSBlbHNlIG0uZ3JvdXAoKSwgcykKCnByaW50IChycyk=