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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 get_file(self, user, handle):
 """Retrieve a file for a user. :returns: a :class:`pathlib.Path` instance to this file, or None if no file can be found for this handle. """

        user_dir = self.user_dir(user)
        if not user_dir.exists():
            return None

        if not is_valid_handle(handle):
            return None

        file_path = user_dir / handle

        if not file_path.exists() and not file_path.is_file():
            return None

        return file_path