@classmethod<EOL><INDENT>def from_filename(cls, filename, start_byte, chunk_size, callbacks=None,<EOL>enable_callbacks=True):<DEDENT>
f = open(filename, '<STR_LIT:rb>')<EOL>f.seek(start_byte)<EOL>file_size = os.fstat(f.fileno()).st_size<EOL>return cls(f, chunk_size, file_size, callbacks, enable_callbacks)<EOL>
Convenience factory function to create from a filename.

        :type start_byte: int
        :param start_byte: The first byte from which to start reading.

        :type chunk_size: int
        :param chunk_size: The max chunk size to read.  Trying to read
            pass the end of the chunk size will behave like you've
            reached the end of the file.

        :type full_file_size: int
        :param full_file_size: The entire content length associated
            with ``fileobj``.

        :type callbacks: function(amount_read)
        :param callbacks: Called whenever data is read from this object.

        :type enable_callbacks: bool
        :param enable_callbacks: Indicate whether to invoke callback
            during read() calls.

        :rtype: ``ReadFileChunk``
        :return: A new instance of ``ReadFileChunk``