>>> import re
>>> s = ["1", "2", "12", "21", "31", "32", "3"]
>>> p = re.compile(r"1|2")
>>> [ x for x in s if not re.match(p, x) is None ]
['1', '2', '12', '21']

 import re
s = ["1", "2", "12", "21", "31", "32", "3", '23', '112211', '1234321']
for i in s:
    res = re.findall('^[12]+$', i)
    print (res)
>>> 
['1']
['2']
['12']
['21']
[]
[]
[]
['112211']
[]
>>>

 p = re.compile('[12]+$')