Flask template loader

gistfile1.py

import os.path

from jinja2 import FileSystemLoader, BaseLoader
from flask import session


class VersionedTemplatesLoader(BaseLoader):

    def __init__(self, app):

        base_template_path = os.path.join(app.root_path, 'templates')

        self._old_templates = FileSystemLoader(
            [os.path.join(base_template_path, 'v0')]
        )
        self._new_templates = FileSystemLoader(
            [os.path.join(base_template_path, 'v1')]
        )

    def get_source(self, environment, template):

        if session.get('use_new_templates', False):
            return self._new_templates.get_source(environment, template)

        return self._old_templates.get_source(environment, template)