install python 3.9 via windows installer on appveyor

Signed-off-by: oleg.hoefling <[email protected]>

Author: hoefling

.appveyor.yml

@@ -11,11 +11,31 @@ environment:
   - python: 38
   - python: 38-x64
   - python: 39
-    image: Visual Studio 2019
+    python_version: 3.9.0
   - python: 39-x64
-    image: Visual Studio 2019
+    python_version: 3.9.0
 
 install:
+  - ps: |
+      # from https://github.com/appveyor/build-images/blob/27bde614bc60d7ef7a8bc46182f4d7582fa11b56/scripts/Windows/install_python.ps1#L88-L108
+      function InstallPythonEXE($targetPath, $version) {
+        $urlPlatform = ""
+        if ($targetPath -match '-x64$') {
+            $urlPlatform = "-amd64"
+        }
+        Write-Host "Installing Python $version$urlPlatform to $($targetPath)..." -ForegroundColor Cyan
+        $downloadUrl = "https://www.python.org/ftp/python/$version/python-$version$urlPlatform.exe"
+        Write-Host "Downloading $($downloadUrl)..."
+        $exePath = "$env:TEMP\python-$version.exe"
+        (New-Object Net.WebClient).DownloadFile($downloadUrl, $exePath)
+        Write-Host "Installing..."
+        cmd /c start /wait $exePath /quiet TargetDir="$targetPath" Shortcuts=0 Include_launcher=1 InstallLauncherAllUsers=1 Include_debug=1
+        Remove-Item $exePath
+        Write-Host "Installed Python $version" -ForegroundColor Green
+      }
+      if ( -not ( Test-Path -Path C:\\Python$env:PYTHON -PathType Container ) ) {
+        InstallPythonEXE C:\\Python$env:PYTHON $env:PYTHON_VERSION
+      }
   - SET PATH=C:\\Python%PYTHON%;c:\\Python%PYTHON%\\scripts;%PATH%
   - python -m pip install -U pip wheel setuptools