flask sqlite jinja accessing and updating database help

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Is my code 2.7? on my computer

Your error message dos reveal that you use Python 2.7.
Has to use python3 to execute code,python will call Python 2.7.

Error:
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 2292, in wsgi_app

I use pyenv always for my setup on Linux,can look at setup here.
A older tutorial with Python 3.5 on Mint 18.
Raspbian OS Python 3.