import re
# Compile a regular expression pattern into a regular expression object, which can be used for matching using its match(), search() and other methods, described below.
prog = re.compile(pattern)
result = prog.match(string)
# is equivalent to
result = re.match(pattern, string)
import re
>>> m = re.search('(?<=abc)def', 'abcdef')
>>> m.group(0)
'def'
exp = "(\d{1,3}\.){3}\d{1,3}"
ip = "blah blah 192.168.0.185 blah blah"
match = re.search(exp, ip)
print match.group()