Radio buttons widget for boolean field

Question

When I add new boolean field to content type in admin i can choose widget for it: checkbox or radio buttons. How can I describe it in code? When I do something like this there is no widget:

$i = 1; 
foreach($questions as $question){
        $field_name = $name . '_q' . $i;
        $fields[$field_name] = array(
            'field_name' => $field_name,
            'type' => 'list_boolean',
            'required' => true,
        );
        $i++;
}

foreach($fields as $field){
        if (!field_info_field($field['field_name'])) {
            field_info_cache_clear();
            field_create_field($field);
        }
}

$instances = array();

$i = 1;
foreach($questions as $question){
    $field_name = $name . '_q' . $i;
    $instances[$field_name] = array(
        'field_name' => $field_name,
        'label' => $question,
        'widget' => array(
            'type' => 'radio'
         ),
         'required' => true
     );
     $i++;
}

foreach($instances as $instance){
    $instance['entity_type'] = 'node';
    $instance['bundle'] = $name;
    field_create_instance($instance);
}

Answer 1

Simplest way is to use field_create_field() to create the field itself and field_create_instance($instance) to have an instance for your content type. Widget type should be set in $instance['widget']['type'] sent to field_create_instance($instance).

Taken from this answer.