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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 write(self, fptr):
 """Write a data entry url box to file. """

        # Make sure it is written out as null-terminated.
        url = self.url
        if self.url[-1] != chr(0):
            url = url + chr(0)
        url = url.encode()

        length = 8 + 1 + 3 + len(url)
        write_buffer = struct.pack('>I4sBBBB',
                                   length, b'url ',
                                   self.version,
                                   self.flag[0], self.flag[1], self.flag[2])
        fptr.write(write_buffer)
        fptr.write(url)