Example setup script for the Mage2Kata episode 13: The Event Observer Kata.

UpgradeData.php

<?php

namespace Mage2Kata\EventObserver\Setup;

use Magento\Catalog\Model\Product;
use Magento\Eav\Setup\EavSetup;
use Magento\Framework\Setup\ModuleContextInterface;
use Magento\Framework\Setup\ModuleDataSetupInterface;
use Magento\Framework\Setup\UpgradeDataInterface;

class UpgradeData implements UpgradeDataInterface
{
    /**
     * @var EavSetup
     */
    private $eavSetup;

    public function __construct(EavSetup $eavSetup)
    {
        $this->eavSetup = $eavSetup;
    }

    public function upgrade(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
    {
        $this->eavSetup->addAttribute(Product::ENTITY, 'magento_se_points', [
            'label'            => 'Magento SE Points Value',
            'type'             => 'int',
            'required'         => 0,
            'user_defined'     => 1,
            'comparable'       => 1,
            'visible_on_front' => 1,
            'is_configurable'  => 0,
            'group'            => 'Product Details',
        ]);
    }
}