I strongly advise you to read the official guide on deploying a Python web app to Azure App Service using CI/CD.
Regardless of whether you're using Azure Devops or not, you'll need to identify your dependencies in requirements.txt and link them to the appropriate environment. You must define a job in Azure Devops to install the requirements from the file specified above.
- task: UsePythonVersion@0
displayName: 'Use Python $(pythonVersion)'
- script: |
python -m venv antenv
python -m pip install --upgrade pip
pip install setup
pip install -r requirements.txt
displayName: "Install requirements"