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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 ftp_url(self):
 # type: () -> Text """Get the FTP url this filesystem will open."""

        url = (
            "ftp://{}".format(self.host)
            if self.port == 21
            else "ftp://{}:{}".format(self.host, self.port)
        )
        return url