>>> import re
>>> instr = 'nudge dudge http://hodge.podge/dodge fudge'
>>> ptn = re.compile('(http://[^¥ ]*)')
>>> ptn.sub('<a href=¥¥1>¥¥1</a>', instr)
'nudge dudge <a href=http://hodge.podge/dodge>;http://hodge.podge/dodge<;/a> fudge'