<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def transform_lines(self, line_index_iterator, transform_callback):
 """ Transforms the text on a range of lines. When the iterator yield an index not in the range of lines that the document contains, it skips them silently. To uppercase some lines:: new_text = transform_lines(range(5,10), lambda text: text.upper()) :param line_index_iterator: Iterator of line numbers (int) :param transform_callback: callable that takes the original text of a line, and return the new text for this line. :returns: The new text. """

        # Split lines
        lines = self.text.split('\n')

        # Apply transformation
        for index in line_index_iterator:
            try:
                lines[index] = transform_callback(lines[index])
            except IndexError:
                pass

        return '\n'.join(lines)