>>> import re
>>> myString = "HI there. You should higher that person for the job. Hi hi."
>>> keyword = "hi"
>>> search = re.compile(r'b(%s)b' % keyword, re.I)
>>> search.sub('<b>\1</b>', myString)
'<b>HI</b> there. You should higher that person for the job. <b>Hi</b> <b>hi</b>.'

import re

def SurroundWith(text, keyword, before, after):
  regex = re.compile(r'b%sb' % keyword, re.IGNORECASE)
  return regex.sub(r'%s%s' % (before, after), text)

>>> SurroundWith('HI there. You should hire that person for the job. '
...              'Hi hi.', 'hi', '<b>', '</b>')
'<b>HI</b> there. You should hire that person for the job. <b>Hi</b> <b>hi</b>.'

def SurroundWith2(text, keyword, before, after):
  regex = re.compile(r'([^a-zA-Z0-9])(%s)([^a-zA-Z0-9])' % keyword,
                     re.IGNORECASE)
  return regex.sub(r'1%s2%s3' % (before, after), text)

import re
def reg(keyword, myString) :
   regx = re.compile(r'b(' + keyword + r')b', re.IGNORECASE)
   return regx.sub(r'<b>1</b>', myString)