jinja2.exceptions.TemplateNotFound: bootstrap/base.html
You need to import Bootstrap in this way below:
from flask_bootstrap import Bootstrap
...
bootstrap = Bootstrap(app)
flask.ext.bootstrap is deprecated
The answer is correct.
You can test settings in the execution file, for example: flaskr/flaskr.py
from flask_bootstrap import Bootstrap
....
app = Flask(__name__)
bootstrap = Bootstrap(app)
db = SQLAlchemy(app)
The problem should have been solved.