code: def _init_filename(self, filename=None, ext=None):
          
  
          extension = ext or self.default_extension
          filename = self.filename(filename, ext=extension, use_my_ext=True, set_default=True)
          #: Current full path of the object for reading and writing I/O.
          self.real_filename = os.path.realpath(filename)
docs: Initialize the current filename :attr:`FileUtils.real_filename` of the object.
  
          Bit of a hack.
  
          - The first invocation must have ``filename != None``; this will set a
            default filename with suffix :attr:`FileUtils.default_extension`
            unless another one was supplied.
  
          - Subsequent invocations either change the filename accordingly or
            ensure that the default filename is set with the proper suffix.