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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 add_text(self, end, next=None):
 """ Adds the text from string beginning to the specified ending index to the format. :param end: The ending index of the string. :param next: The next string begin index. If None, the string index will not be updated. """


        if self.str_begin != end:
            self.fmt.append_text(self.format[self.str_begin:end])

        if next is not None:
            self.str_begin = next