Tal: If you want to verify your is_id_char function, you could use the code

for i in range(65536):
    c = chr(i)
    c2 = 'a'+c
    if is_id_char(c) != c2.isidentifier():
        print('\\u%.4x'%i,is_id_char(c),c2.isidentifier())

Alternatively, you could use the strategy taken in that code for is_id_char itself:

def is_id_char(c):
  return ('a'+c).isidentifier()