r before a python String

One more important detail we’ve introduced here is that r character in front of the regular expression string. This tells Python that the string is a “raw string” – its contents should not interpret backslashes. In normal Python strings, backslashes are used for escaping special characters – such as in the string '\n', which is a one-character string containing a newline. When you add the r to make it a raw string, Python does not apply its backslash escaping – so, r'\n' is a two-character string containing a literal backslash and a lowercase “n”. There’s a natural collision between Python’s usage of backslashes and the backslashes that are found in regular expressions, so it’s strongly suggested that you use raw strings any time you’re defining a regular expression in Python. From now on, all of the URLpatterns in this book will be raw strings.