import re
prefixes = ['mr', 'smr']
regex = r'\b(?:' + '|'.join(prefixes) + ')\.\s*'
i = 'hi mr.john, smr. john, etc. Previous etc should not be removed'
i = re.sub(regex,'',i)
print(i)
aW1wb3J0IHJlCgpwcmVmaXhlcyA9IFsnbXInLCAnc21yJ10KcmVnZXggPSByJ1xiKD86JyArICd8Jy5qb2luKHByZWZpeGVzKSArICcpXC5ccyonCmkgPSAnaGkgbXIuam9obiwgc21yLiBqb2huLCBldGMuIFByZXZpb3VzIGV0YyBzaG91bGQgbm90IGJlIHJlbW92ZWQnCmkgPSByZS5zdWIocmVnZXgsJycsaSkKcHJpbnQoaSkK