%%javascript

$("#renumber-button").parent().remove();

function renumber() {
    // renumber cells in order, so it doesn't look like you made any mistakes
    var i=1;
    IPython.notebook.get_cells().map(function (cell) {
        if (cell.cell_type == 'code') {
            // set the input prompt
            cell.set_input_prompt(i);
            // set the output prompt (in two places)
            cell.output_area.outputs.map(function (output) {
                if (output.output_type == 'execute_result') {
                    output.execution_count = i;
                    cell.element.find(".output_prompt").text('Out[' + i + ']:');
                }
            });
            i += 1;
        }
    });
}

IPython.toolbar.add_buttons_group([{
  'label'   : 'Renumber',
  'icon'    : 'fa-list-ol',
  'callback': renumber,
  'id'      : 'renumber-button'
}]);

time.time() - start

time.time() - start

len(In)