Create a tab trigger / shortcut for Sublime Text to spit out @include when you type 'in' then hit tab. Go to Tools > New Snippet. Save this in Packages > User.

at-include.sublime-snippet

<snippet>
  <content><![CDATA[
@include 
]]></content>
  <!-- Optional: Set a tabTrigger to define how to trigger the snippet -->
  <tabTrigger>in</tabTrigger> 
  <!-- Optional: Set a scope to limit where the snippet will trigger -->
  <!-- <scope>source.scss</scope> -->
</snippet>

Is source.python on purpose?

Here's mine:

Include

<snippet>
  <content><![CDATA[
@include ${1}
]]></content>
  <!-- Optional: Set a tabTrigger to define how to trigger the snippet -->
  <tabTrigger>inc</tabTrigger>
  <!-- Optional: Set a scope to limit where the snippet will trigger -->
  <scope>source.scss</scope>
</snippet>

Extend

<snippet>
  <content><![CDATA[
@extend %${1};${2}
]]></content>
  <!-- Optional: Set a tabTrigger to define how to trigger the snippet -->
  <tabTrigger>ext</tabTrigger>
  <!-- Optional: Set a scope to limit where the snippet will trigger -->
  <scope>source.scss</scope>
</snippet>

Fixed. Good catch.

👍