Generally it’s still better to call close() or use the with statement, because there may be some unexpected behaviour in special circumstances. For example, the expat-IncrementalParser seems to expect a file to be closed, or it won’t return the last tidbit of parsed xml until a timeout occurs in some rare circumstances.
But for the with-statement, which handles the closing for you, you have to use the StringIO class from the io-Modules, as stated in the comment of Ivc.
This was a major headache in some legacy sax-parser script we solved by closing the StringIO manually.
The “out-of-scope” close didn’t work. It just waited for the timeout-limit.