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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 _set_initial_contents(self, contents):
 """Sets the file contents and size. Called internally after initial file creation. Args: contents: string, new content of file. Returns: True if the contents have been changed. Raises: IOError: if the st_size is not a non-negative integer, or if st_size exceeds the available file system space """

        contents = self._encode_contents(contents)
        changed = self._byte_contents != contents
        st_size = len(contents)

        if self._byte_contents:
            self.size = 0
        current_size = self.st_size or 0
        self.filesystem.change_disk_usage(
            st_size - current_size, self.name, self.st_dev)
        self._byte_contents = contents
        self.st_size = st_size
        self.epoch += 1
        return changed