Access HTML attribute value in SASS

Question

Is it possible to access an HTML attribute value in SASS? I have a line of code that says

<ul id="my_id" data-count="3">

where the 3 is the result of some jQuery stuff. I need the 3 to calculate some CSS. How can I save it as a SASS variable?

Alternatively, is there a way of counting the number of child elements of a certain parent element? Say I have this code:

<ul id="my_id" data-count="3">
    <li>First list item</li>
    <li>Second list item</li>
    <li>Third list item</li>
</ul>

(As you might have guessed, the value of data-count matches the number of list items.) Can SASS count the list items and save that number as a variable?

Any ideas would be greatly appreciated.