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I have create product attribute of type select select with below configurations:

$setup->addAttribute(MagentoCatalogModelProduct::ENTITY, 'attribute_code', [

            'attribute_model' => NULL,

            'backend' => '',

            'type' => 'int',

            'table' => '',

            'frontend' => '',

            'input' => 'select',

            'label' => 'Custom Attribute',

            'frontend_class' => '',

            'source' => '',

            'required' => true,

            'user_defined' => '1',

            'default' => 0,

            'unique' => '0',

            'note' => '',

            'input_renderer' => NULL,

            'global' => '1',

            'visible' => '1',

            'searchable' => '0',

            'filterable' => '1',

            'comparable' => '1',

            'visible_on_front' => '1',

            'is_html_allowed_on_front' => '0',

            'is_used_for_price_rules' => '1',

            'filterable_in_search' => '1',

            'used_in_product_listing' => '0',

            'used_for_sort_by' => '0',

            'is_configurable' => '1',

            'position' => '1',

            'wysiwyg_enabled' => '0',

            'used_for_promo_rules' => '1',

            'option' =>

                array(

                    'values' => $options,

                ),

            ]

        );

How to set default value of this custom attribute?

Use below code in:
Vendor/Module/Setup/InstallData.php or Vendor/Module/Setup/UpgradeData.php

$eavSetup = $this->eavSetupFactory->create(['setup' => $setup]);

       $eavSetup->addAttribute(

               MagentoCatalogModelProduct::ENTITY,

           'international',

           [

               'group' => 'General',

               'type' => 'int',

               'label' => 'International',

               'backend' => '',

               'input' => 'select',

               'wysiwyg_enabled'   => false,

               'source' => 'NamespaceModuleNameModelConfigSourceYesNo',

               'required' => true,

               'sort_order' => 15,

               'global' => MagentoCatalogModelResourceModelEavAttribute::SCOPE_GLOBAL,

               'used_in_product_listing' => false,

               'visible_on_front' => false,

       ]

   );



   $setup->endSetup();

Source file mentioned above so by defaulty value will be set

class YesNo extends MagentoEavModelEntityAttributeSourceAbstractSource

{

    protected $_options;



    /**

     * getAllOptions

     *

     * @return array

     */

    public function getAllOptions()

    {

        if ($this->_options === null) {

            $this->_options = [

                ['value' => '0', 'label' => __('No')],

                ['value' => '1', 'label' => __('Yes')]

            ];

        }

        return $this->_options;

    }

    final public function toOptionArray()

    {

       return array(

        array('value' => '0', 'label' => __('No')),

        array('value' => '1', 'label' => __('Yes'))

    );

   }

}