foo.py

from jinja2 import Template

source = """
{%- set foo = 'hello' -%}

{%- macro bar(things, oid, attribute) -%}
  {%- for thing in things -%}
    {%- if thing.offer_id == oid -%}
      {{attr thing attribute}}
    {%- endif -%}
  {%- endfor -%}
{%- endmacro -%}

{% set foo = bar(widgets) %}

{{ foo }}
{{ foo }}
{{ foo }}
"""
template = Template(source)

widgets = (1, 2, 3, 4)

rendered = template.render(widgets=widgets)
print rendered