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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 url(self, filetype, base_dir=None, sasdir='sas', **kwargs):
 """Return the url of a given type of file. Parameters filetype : str File type parameter. Returns ------- full : str The sas url to the file. """


        location = self.location(filetype, **kwargs)
        return join(self.remote_base, sasdir, location) if self.remote_base and location else None