AttributeError Regex

[linh_py]

hello everybody, i'm learning python, use re module, and i had a error, help me please.

import re
numRegex=re.compile(r"^\d{1,3}(,(\d{3}))*$")
mo = numRegex.search(" 12,124,123,221  ")
print(mo.group())

=> AttributeError: 'NoneType' object has no attribute 'group'