Create and return a temporary file.
Arguments:
'prefix', 'suffix', 'directory' -- as for mkstemp.
'mode' -- the mode argument to os.fdopen (default "w+b").
'bufsize' -- the buffer size argument to os.fdopen (default -1).
The file is created as mkstemp() would do it.
Returns an object with a file-like interface. The file has no
name, and will cease to exist when it is closed.