def create_code_cell(block):
        """Create a notebook code cell from a block."""
        code_cell = nbbase.new_code_cell(source=block['content'])

        attr = block['attributes']
        if not attr.is_empty:
            code_cell.metadata \
                = nbbase.NotebookNode({'attributes': attr.to_dict()})
            execution_count = attr.kvs.get('n')
            if not execution_count:
                code_cell.execution_count = None
            else:
                code_cell.execution_count = int(execution_count)

        return code_cell
Create a notebook code cell from a block.