Azure App Service provides us with a fully-managed platform for us to run our web apps. We can deploy ASP.NET web apps quickly to Azure without any complicated configurations. However, if we are working with a Python web app with Flask and want to deploy the app to Azure, we have to do some configurations both on Azure Web Service and the Python app.

First, install Python extension for the App Service since the built-in Python environment cannot be modified, not even installing a third-party package from pip.

Go to Extensions - Add and install a Python environment.

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Copy the install path after the installation.

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Now that we finished the configuration, the next step is to configure your Python app. In order to run a Python web app in the production environment, we need to host your app on a WSGI server. In this passage, we are going to use Waitress as WSGI server.

Create a Python file named "run_waitress_server.py" and paste the code below to this file.

import os
from waitress import serve
from your_app import app

serve(app,host="0.0.0.0",port=os.environ["PORT"])

Then, create a "web.config" with the code below.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
 <system.webServer>
  <handlers>
   <add name="httpPlatformHandler" path="*" verb="*" 
         modules="httpPlatformHandler" resourceType="Unspecified" />
  </handlers>

  <httpPlatform processPath="D:\home\python364x64\python.exe"
 arguments="run_waitress_server.py" requestTimeout="00:04:00" startupTimeLimit="120" startupRetryCount="3" stdoutLogEnabled="true">
   <environmentVariables>
        <environmentVariable name="PYTHONPATH" value="D:\home\site\wwwroot" />
        <environmentVariable name="PORT" value="%HTTP_PLATFORM_PORT%" />
   </environmentVariables>
  </httpPlatform>
 </system.webServer>
</configuration>

Notice that "processPath" should point to your Python environment.

Finally, to make your app deploy smoothly, we can create a "requirements.txt" and a deploy script which can help us install the required packages automatically during the deployment process.

".deployment" file:

[config]
command = deploy.cmd

"deployment.cmd" file:

@if "%SCM_TRACE_LEVEL%" NEQ "4" @echo off

:: ----------------------
:: KUDU Deployment Script
:: Version: 1.0.16
:: ----------------------

:: Prerequisites
:: -------------

:: Verify node.js installed
where node 2>nul >nul
IF %ERRORLEVEL% NEQ 0 (
  echo Missing node.js executable, please install node.js, if already installed make sure it can be reached from current environment.
  goto error
)

:: Setup
:: -----

setlocal enabledelayedexpansion

SET ARTIFACTS=%~dp0%..\artifacts

IF NOT DEFINED DEPLOYMENT_SOURCE (
  SET DEPLOYMENT_SOURCE=%~dp0%.
)

IF NOT DEFINED DEPLOYMENT_TARGET (
  SET DEPLOYMENT_TARGET=%ARTIFACTS%\wwwroot
)

IF NOT DEFINED NEXT_MANIFEST_PATH (
  SET NEXT_MANIFEST_PATH=%ARTIFACTS%\manifest

  IF NOT DEFINED PREVIOUS_MANIFEST_PATH (
    SET PREVIOUS_MANIFEST_PATH=%ARTIFACTS%\manifest
  )
)

IF NOT DEFINED KUDU_SYNC_CMD (
  :: Install kudu sync
  echo Installing Kudu Sync
  call npm install kudusync -g --silent
  IF !ERRORLEVEL! NEQ 0 goto error

  :: Locally just running "kuduSync" would also work
  SET KUDU_SYNC_CMD=%appdata%\npm\kuduSync.cmd
)
goto Deployment

:: Utility Functions
:: -----------------

:SelectPythonVersion

IF DEFINED KUDU_SELECT_PYTHON_VERSION_CMD (
  call %KUDU_SELECT_PYTHON_VERSION_CMD% "%DEPLOYMENT_SOURCE%" "%DEPLOYMENT_TARGET%" "%DEPLOYMENT_TEMP%"
  IF !ERRORLEVEL! NEQ 0 goto error

  SET /P PYTHON_RUNTIME=<"%DEPLOYMENT_TEMP%\__PYTHON_RUNTIME.tmp"
  IF !ERRORLEVEL! NEQ 0 goto error

  SET /P PYTHON_VER=<"%DEPLOYMENT_TEMP%\__PYTHON_VER.tmp"
  IF !ERRORLEVEL! NEQ 0 goto error

  SET /P PYTHON_EXE=<"%DEPLOYMENT_TEMP%\__PYTHON_EXE.tmp"
  IF !ERRORLEVEL! NEQ 0 goto error

  SET /P PYTHON_ENV_MODULE=<"%DEPLOYMENT_TEMP%\__PYTHON_ENV_MODULE.tmp"
  IF !ERRORLEVEL! NEQ 0 goto error
) ELSE (
  SET PYTHON_RUNTIME=python-2.7
  SET PYTHON_VER=2.7
  SET PYTHON_EXE=%SYSTEMDRIVE%\python27\python.exe
  SET PYTHON_ENV_MODULE=virtualenv
)

goto :EOF

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
:: Deployment
:: ----------

:Deployment
echo Handling python deployment.

:: 1. KuduSync
IF /I "%IN_PLACE_DEPLOYMENT%" NEQ "1" (
  call :ExecuteCmd "%KUDU_SYNC_CMD%" -v 50 -f "%DEPLOYMENT_SOURCE%" -t "%DEPLOYMENT_TARGET%" -n "%NEXT_MANIFEST_PATH%" -p "%PREVIOUS_MANIFEST_PATH%" -i ".git;.hg;.deployment;deploy.cmd"
  IF !ERRORLEVEL! NEQ 0 goto error
)

IF NOT EXIST "%DEPLOYMENT_TARGET%\requirements.txt" goto postPython
IF EXIST "%DEPLOYMENT_TARGET%\.skipPythonDeployment" goto postPython

echo Detected requirements.txt.  You can skip Python specific steps with a .skipPythonDeployment file.

:: 2. Select Python version
call :SelectPythonVersion

pushd "%DEPLOYMENT_TARGET%"

:: 3. Create virtual environment
IF NOT EXIST "%DEPLOYMENT_TARGET%\env\azure.env.%PYTHON_RUNTIME%.txt" (
  IF EXIST "%DEPLOYMENT_TARGET%\env" (
    echo Deleting incompatible virtual environment.
    rmdir /q /s "%DEPLOYMENT_TARGET%\env"
    IF !ERRORLEVEL! NEQ 0 goto error
  )

  echo Creating %PYTHON_RUNTIME% virtual environment.
  %PYTHON_EXE% -m %PYTHON_ENV_MODULE% env
  IF !ERRORLEVEL! NEQ 0 goto error

  copy /y NUL "%DEPLOYMENT_TARGET%\env\azure.env.%PYTHON_RUNTIME%.txt" >NUL
) ELSE (
  echo Found compatible virtual environment.
)

:: 4. Install packages
echo Pip install requirements.
D:\home\python364x64\python.exe -m pip install -r requirements.txt
IF !ERRORLEVEL! NEQ 0 goto error

REM Add additional package installation here
REM -- Example --
REM env\scripts\easy_install pytz
REM IF !ERRORLEVEL! NEQ 0 goto error

:: 5. Copy web.config
IF EXIST "%DEPLOYMENT_SOURCE%\web.%PYTHON_VER%.config" (
  echo Overwriting web.config with web.%PYTHON_VER%.config
  copy /y "%DEPLOYMENT_SOURCE%\web.%PYTHON_VER%.config" "%DEPLOYMENT_TARGET%\web.config"
)

:: 6. Django collectstatic
IF EXIST "%DEPLOYMENT_TARGET%\manage.py" (
  IF EXIST "%DEPLOYMENT_TARGET%\env\lib\site-packages\django" (
    IF NOT EXIST "%DEPLOYMENT_TARGET%\.skipDjango" (
      echo Collecting Django static files. You can skip Django specific steps with a .skipDjango file.
      IF NOT EXIST "%DEPLOYMENT_TARGET%\static" (
        MKDIR "%DEPLOYMENT_TARGET%\static"
      )
      env\scripts\python manage.py collectstatic --noinput --clear
    )
  )
)

popd

:postPython

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
goto end

:: Execute command routine that will echo out when error
:ExecuteCmd
setlocal
set _CMD_=%*
call %_CMD_%
if "%ERRORLEVEL%" NEQ "0" echo Failed exitCode=%ERRORLEVEL%, command=%_CMD_%
exit /b %ERRORLEVEL%

:error
endlocal
echo An error has occurred during web site deployment.
call :exitSetErrorLevel
call :exitFromFunction 2>nul

:exitSetErrorLevel
exit /b 1

:exitFromFunction
()

:end
endlocal
echo Finished successfully.

With everything done, we should be able to deploy your app to Azure now. I used Git but other methods should work as well.