Python string substitution using dictionaries

import re

sub_dict = {
    '%AAA%': 'Hello',
    '%BBB%': 'world'
}

pattern = '|'.join(sub_dict.keys())
repl_func = lambda matchobj: sub_dict[matchobj.group(0)]


text = "%AAA%, the %BBB% !"

text = re.sub(pattern, repl_func, text)

References :
Re: [問題] Python全文取代 - 看板 Python - 批踢踢實業坊