'String' module object has no attribute 'join'

You are trying to use the join method from the string module when you should be using it from the str object.

string.join(current_string,"")

that line for example should be

"".join(current_string)

where current_string is an iteratible.

Just a quick example on how the .join method works

", ".join(['a','b','c'])

will give you a str object of the letters a b and c separated by a comma and a space.