pure: provide more correct implementation of posixfile for Windows requires ctypes Why is posixfile a class? Because the implementation needs to use the Python library call os.fdopen [1], which sets the 'name' attribute on the Python file object it creates to the mostly meaningless string '<fdopen>', since file descriptors don't have a name. But users of posixfile depend on the name attribute [2] being set to a proper value, like Python's built-in 'open' function sets it on file objects. Python file's name attribute is read-only, so we can't just assign to it after the file object has alrady been created. To solve this problem, we save the name of the file on a wrapper object, and delegate the file function calls to the wrapped (private) file object using __getattr__. [1] http://docs.python.org/library/os.html#os.fdopen [2] http://docs.python.org/library/stdtypes.html#file.name