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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(self, path_info):
 """Gets the checksum for the specified path info. Checksum will be retrieved from the state database if available. Args: path_info (dict):
 path info to get the checksum for. Returns: str or None: checksum for the specified path info or None if it doesn't exist in the state database. """

        assert path_info["scheme"] == "local"
        path = path_info["path"]

        if not os.path.exists(path):
            return None

        actual_mtime, actual_size = get_mtime_and_size(path)
        actual_inode = get_inode(path)

        existing_record = self.get_state_record_for_inode(actual_inode)
        if not existing_record:
            return None

        mtime, size, checksum, _ = existing_record
        if self._file_metadata_changed(actual_mtime, mtime, actual_size, size):
            return None

        self._update_state_record_timestamp_for_inode(actual_inode)
        return checksum