You can set a counter in a for loop using:

{% set vars={'value': 0} %}

{% for month in range(0,12) %}
        {% if vars.update({'value': vars['value'] + 1 }) %}{% endif %}
{% endfor %}

If we want the graph just as an svg (you wont be able to print it) you have to add this code to de controller:

chart = bar_chart.render(is_unicode=True)

and in the template:

{{ chart|safe }}

But if you want to generate a PNG on the fly:

chart = b64encode(bar_chart ...

The Flask-Migrate plugin allows using an shell interface for Alembic

With Alembic you can manage changes in the database model providing a version control tool and easing the recreation of the database on any design change

$ python manage.py db init