re in python

http://docs.python.org/library/re.html undersrtanding:

 

Regular expressions use the backslash character ('/') to indicate special forms or to allow special characters to be used without invoking their special meaning. This collides with Python’s usage of the same character for the same purpose in string literals; for example, to match a literal backslash, one might have to write '////' as the pattern string, because the regular expression must be //, and each backslash must be expressed as // inside a regular Python string literal.

 

so in python, since for a string, if you want to express '/', it will be '//',  thus if you want to match the '/' in the string, you may have to write '////' so that it can work for the regular expression. It is horrible. Then we decided to use 'raw'

 

The solution is to use Python’s raw string notation for regular expression patterns; backslashes are not handled in any special way in a string literal prefixed with 'r'. So r"/n" is a two-character string containing '/' and 'n', while "/n" is a one-character string containing a newline. Usually patterns will be expressed in Python code using this raw string notation.