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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 path(self):
 """Return the path to the file, if the ref is a file"""


        if not isinstance(self.ref, str):
            return None

        u = parse_app_url(self.ref)

        if u.inner.proto != 'file':
            return None

        return u.path