How do I debug Flask App in VS Code

Question

I've been trying to get the debugger working in VS Code so that I can debug my Flask App. I have tries so many options in the launch.json that I feel there isn't any left.

the following examples did not work: https://github.com/DonJayamanne/pythonVSCode/wiki/Debugging:-Flask

Debug Flask(Python) web application in Visual studio code

Below are my launch.json and setting.json. I have two configurations in the launch file as I was trying multiple variations.

launch.json

"version": "0.2.0",
    "configurations": [
    {
        "name": "Flask",
        "type": "python",
        "request": "launch",
        "stopOnEntry": false,
        "pythonPath": "${config:python.pythonPath}",
        //"module": "flask.cli",
        "program": "${workspaceRoot}/startup.py",
        "cwd": "${workspaceRoot}",
        "env": {
          "FLASK_APP": "${workspaceRoot}/apt-flask.py",
        },
        "args": [
          "run",
          "--no-debugger",
          "--no-reload"
        ],
        "envFile": "${workspaceRoot}/.env",
        "debugOptions": [
          "WaitOnAbnormalExit",
          "WaitOnNormalExit",
          "RedirectOutput"
        ]
    },
    {
        "name": "Python: APT FLask",
        "type": "python",
        "request": "launch",
        "stopOnEntry": true,
        "pythonPath": "${workspaceFolder}/venv/Scripts/python.exe",
        //"program": "${workspaceFolder}/venv/Scripts/flask.exe",
        "module": "flask.cli",
        "cwd": "${workspaceFolder}",
        "env": {
            "FLASK_APP": "${workspaceFolder}/apt-flask.py",
            "DEBUG": 1,
            "LC_ALL": "en_US.utf-8",
            "LANG": "en_US.utf-8"
        },
        "args": [
            "run",
            "--no-debugger",
            "--no-reload"
        ],
        "envFile": "${workspaceFolder}/.env",
        "debugOptions": [
            "WaitOnAbnormalExit",
            "WaitOnNormalExit",
            "RedirectOutput"
        ]
    }
]

settings.json

{
    "python.pythonPath": "${workspaceRoot}/venv/Scripts/python.exe"
}

As far as errors go, I get no errors in the console, only the error within the editor that tells me that the "Debug adapter process has terminated unexpectedly".

I'm not sure what else to try. I currently use Pycharm but was looking for an editor that is more lightweight and as I use VS Code for other things it makes sense to change, so would be nice to finally get this working.

Any help would be brilliant.

We fixed some default settings to the Flask debugger configuration in the .2018.2.0 release that went out just over 2 hours ago. Please update and see if that new configuration works for you. — Brett Cannon
– Brett Cannon, Commented Mar 8, 2018 at 20:11
@BrettCannon. Updating VS Code has worked. I had to delete the entire launch.json and reload the python default configurations, changed "FLASK_APP": "${workspaceFolder}/apt-flask.py" and is now working as expected!. Thank you — demonLaMagra
– demonLaMagra, Commented Mar 9, 2018 at 10:12

SpeedCoder5 · Accepted Answer · 2019-11-12 22:19:24Z

As of November 2019 I the found the following useful:

New Way (basic & flakey) - "Old Way" Below is Better

https://code.visualstudio.com/docs/python/tutorial-flask

Assuming a simple app.py such as:

import flask
app = flask.Flask(__name__)
@app.route('/')
def index():
    return "Hello world!"

And .vscode/launch.json added to your project by adding Python Flask Debug Configuration from the Debug Explorer drop down.

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Python: Flask",
            "type": "python",
            "request": "launch",
            "module": "flask",
            "env": {
                "FLASK_APP": "app.py",
                "FLASK_ENV": "development",
                "FLASK_DEBUG": "1"
            },
            "args": [
                "run",
                "--no-debugger",
                "--no-reload"
            ],
            "jinja": true
        }
    ]
}

The Flask app is effectively run the "new way" from the VS Code debugger [F5].

python -m flask run

Old Way (better)

Miguel suggests running apps the old way, with additional flags, is better in the VS Code debugger.

Add the following to app.py (from above):

if __name__ == '__main__':
    app.run(use_debugger=False, use_reloader=False, passthrough_errors=True)

Modify .vscode/launch.json to look as follows:

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Python: Flask",
            "type": "python",
            "request": "launch",
            "module": "app",
            "env": {
                "FLASK_APP": "app.py",
                "FLASK_ENV": "development",
                "FLASK_DEBUG": "1"
            },
            "args": [
                // "run",
                // "--no-debugger",
                // "--no-reload"
            ],
            "jinja": true
        }
    ]
}

So the Flask app is effectively run the "old way" from the VS Code debugger [F5].

python app.py

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