How locate :: Before element in Selenium Python

I'm using Selenium Python to locate label element.I want to use ::before to locate it,because this is a pop window.

<div class="crow" grp="0" grpname="Pizza Size">
    ::before
    <label class="label0" cid="1">
    <input type="radio" name="0" coname="M" sname="" price="9.99" value="392">M<b class="ip">9.99</b>
    </label>
    <label class="label0" cid="1"><input type="radio" name="0" coname="L" sname="" price="11.99" value="393">L<b class="ip">11.99</b>
    </label><div style="clear:both">
    </div>
    </div>

I have no idea how to use ::before to locate it,any friend can help?