Update Python and Flask usage in Compose tutorial #8609
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* Uses the modern Python 3.7 image, as 3.4 is EOL. * Separates copying and installing requirements from copying project, to make rebuilds more efficient. * Uses the recommended `flask run` command. This is especially needed on Windows, where `app.py` incorrectly looks like an executable file when copying into Docker. * Uses the `FLASK_ENV` env var to control development mode.
This is not needed when using the recommended `flask run` command to run the development server.
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davidism
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bermudezmt
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Thanks for the PR @davidism!
Just a couple of minor changes.
| * Install the Python dependencies. | ||
| * Set the default command for the container to `python app.py`. | ||
| * Set environment variables used by the `flask` command. | ||
| * Install gcc so Python packages such as MarkupSafe and SQLAlchemy can compile speedups. |
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nit: Since this is just a Compose get started guide, I'm not sure we need to include Python optimisations.
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Since this is one of two official Docker documents introducing devs to using Flask with Docker, I'd rather they get a reasonable experience without having to discover it later, especially since it's non-obvious that speedups are not compiled. Overall I think the focus is still on Compose.
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Do you agree, or would you like me to change something?
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My concern is that we're conflating getting started with Compose and optimising a Python app. That might overload new users with too much information.
I did LGTM the PR though as it's net better than what we have currently.
@usha-mandya is there anything else we need?
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Can't think of anything else, @chris-crone. Thanks.
COPYinstead ofADD, since behavior ofADDis not used, as recommended in theDockerfilereference.flask runcommand. This is especially needed on Windows, whereapp.pyincorrectly looks like an executable file when copying into Docker. 0.15.0 causes OSError: [Errno 8] Exec format error: in Docker for Windows pallets/werkzeug#1482FLASK_ENVenv var to control development mode (debugger, reloader). This is only set when demonstrating thevolumesoption for live updating files, as it should not be used in production. Note that the development server (flask run,app.run()) should not be used in production either, but I think that's outside the scope of this change.