http://docs.python.org/library/io.html#io.StringIO
http://docs.python.org/library/stringio.html
I see this.
An in-memory stream for unicode text. It inherits TextIOWrapper.
This module implements a file-like class, StringIO, that reads and writes a string buffer (also known as memory files).
io.StringIO is a class. It handles Unicode. It reflects the preferred Python 3 library structure.
StringIO.StringIO is a class. It handles strings. It reflects the legacy Python 2 library structure.
What should be preferred?
Always move forward toward the new library organization. The io.open should be used to replace the built-in Unicode-unaware open.
Forward. Move forward.