Pass data to email template from python code Odoo 10

I need to pass objects to email_template from python code:

*.py

def _alert_product_expiry(self):
    alert_data = self.search([('alert_date','=',fields.Date.today())])
    if alert_data:
        template_id = self.env.ref('alert_email_template')// Need to pass `alert_data` to template
        send = template_id.send_mail(self.id, force_send=True)

template_body

  <field name="body_html">
        <![CDATA[
       //Retrieve that object here and perform for loop. I don't know how retrieve it.
]]>

  </field>

How can i do it?