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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def append(self, p_todo, p_string):
 """ Appends a text to the todo, specified by its number. The todo will be parsed again, such that tags and projects in de appended string are processed. """

        if len(p_string) > 0:
            new_text = p_todo.source() + ' ' + p_string
            p_todo.set_source_text(new_text)
            self._update_todo_ids()
            self.dirty = True