jinja2 load template from string: TypeError: no loader for this environment specified

You can provide loader in Environment from that list

from jinja2 import Environment, BaseLoader

rtemplate = Environment(loader=BaseLoader).from_string(myString)
data = rtemplate.render(**data)

Edit: The problem was with myString, it has {% include 'test.html' %} and Jinja2 has no idea where to get template from.

UPDATE

As @iver56 kindly noted, it's better to:

rtemplate = Environment(loader=BaseLoader()).from_string(myString)

When I came to this question, I wanted FileSystemLoader:

from jinja2 import Environment, FileSystemLoader
with open("templates/some_template.html") as f:
    template_str = f.read()
template = Environment(loader=FileSystemLoader("templates/")).from_string(template_str)
html_str = template.render(default_start_page_lanes=default_start_page_lanes,
                           **data)