import os
import tokenize

bla = "#coding:xxx"
fn = "test.py"

with open(fn, "x", encoding="ascii") as fp:
    fp.write(bla)

try:
    f = tokenize.open(fn)
except Exception as err:
    print("tokenize.open failed: %s" % err)
else:
    f.close()

os.unlink(fn)