Run Flask using python3 not python

Question

How can you run Flask app which uses a specific version of python?

On my env "python" = python2.7 and "python3" = python3.6. I have installed Flask using pip3. I start the app with FLASK_APP=app.py flask run. It uses python2.7 to execute, I would like it to use python3.6.

Also tried adding #!flask/bin/python3 to app.py, but it did not have an effect.

Put it in a virtualenv that was created for Python 3. – Nils Werner Mar 13 '18 at 11:44 — Nils Werner, Mar 13 '18 at 11:44
have you considered using Docker? – N. Ivanov Mar 13 '18 at 11:44 — N. Ivanov, Mar 13 '18 at 11:44
`#!flask` isn't a thing. Try `#!/usr/bin/python3` – OneCricketeer Mar 13 '18 at 11:45 — OneCricketeer, Mar 13 '18 at 11:45

score 12 · Accepted Answer · answered Mar 13 '18 at 11:48

12

There are several ways:

Virtualenv lets you create isolated python environments with different versions (this is the way I would recommend)
You can put #!/usr/bin/python3 on top of your python file (see here)
Or you can start your script with python3 script.py
As mentioned in the comments above you can also start your script inside a Docker container that hosts a python3 installation

answered Mar 13 '18 at 11:48

Jonathan R

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Thank you, `#!/usr/bin/python3` worked. I will put it in virtualenv at some point. – Money_Badger Mar 13 '18 at 12:05

score 1 · Answer 2 · answered May 04 '20 at 16:27

What I did was:

which flask, to find flask binary executable path (in my case /home/myuser/.local/bin/flask
edit /home/myuser/.local/bin/flask, changing the first line from #!/usr/bin/python to #!/usr/bin/python3

In summary, making flask use python3, regardless of which shebang was specified in other scripts, since those scripts are not the entrypoint of execution, but flask is. I didn't have to change the shebang in any of my scripts, just the flask executable.

Run Flask using python3 not python

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