import re
inStr0 = "" inStr1 = "aa79bb" inStr2 = "aa78bb"
pat = re.compile(r"^(.(?!79))*$")
pat.search(inStr0)
<re.Match object; span=(0, 0), match=''>
pat.search(inStr1)
pat.search(inStr2)
<re.Match object; span=(0, 6), match='aa78bb'>