on openERP 7 usually I use html to make pdf report. when I need variable, on html I just add

<!-- <% variable1 = 2 %> -->
<!-- <% variable2 = variable1 + 12 %> -->
${ variable2 }

so on pdf will show
14

when I use it on odoo 8, why it became error, the Odoo warning is like this:

Encountered unknown tag 'variable1'. Jinja was looking for the following tags: 'endfor' or 'else'. The innermost block that needs to be closed is 'for'.

<class 'jinja2.exceptions.TemplateSyntaxError'>,Encountered unknown tag 'variable1'. Jinja was looking for the following tags: 'endfor' or 'else'. The innermost block that needs to be closed is 'for'.,<traceback object at 0xb0201694>

what must I do to add a variable?