How to use replace mode for python

Question

There is a sample of regx: "one two" use this regx to \b(\w+)(\s)(\w+)\b replace with $3$2$1 and then get "two one" Now i want to implement this with python re.sub:

s="one two"
print re.sub(r"\b(\w+)(\s)(\w+)\b","$3$2$1",s)

This output $3$2$1, not "two one".How can i do this in python?

Answer 1

You use \number in python for printing a matched result:

>>> s="one two"
>>> print re.sub(r"\b(\w+)(\s)(\w+)\b",r"\3\2\1",s)
two one

Note that you have to make it a raw string, or you would have to do \\3 \\2 \\1 (i.e escape the backslashes)