Install python38/39 on windows

kokoro/release/python/windows/build_artifacts.bat

@@ -62,6 +62,8 @@ SET PYTHON_VERSION=3.7
 SET PYTHON_ARCH=64
 CALL build_single_artifact.bat || goto :error
 
+powershell -File kokoro/release/python/windows/install_python_interpreters.ps1
+
 SET PYTHON=C:\python38_32bit
 SET PYTHON_VERSION=3.8
 SET PYTHON_ARCH=32

kokoro/release/python/windows/install_python_interpreters.ps1

@@ -0,0 +1,97 @@
+#!/usr/bin/env powershell
+# Install Python 3.8 for x64 and x86 in order to build wheels on Windows.
+# Originally from grpc/tools/internal_ci/helper_scripts/install_python_interpreters.ps1
+
+Set-StrictMode -Version 2
+$ErrorActionPreference = 'Stop'
+
+trap {
+    $ErrorActionPreference = "Continue"
+    Write-Error $_
+    exit 1
+}
+
+# Avoid "Could not create SSL/TLS secure channel"
+[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
+
+function Install-Python {
+    Param(
+        [string]$PythonVersion,
+        [string]$PythonInstaller,
+        [string]$PythonInstallPath,
+        [string]$PythonInstallerHash
+    )
+    $PythonInstallerUrl = "https://www.python.org/ftp/python/$PythonVersion/$PythonInstaller.exe"
+    $PythonInstallerPath = "C:\tools\$PythonInstaller.exe"
+
+    # Downloads installer
+    Write-Host "Downloading the Python installer: $PythonInstallerUrl => $PythonInstallerPath"
+    Invoke-WebRequest -Uri $PythonInstallerUrl -OutFile $PythonInstallerPath
+
+    # Validates checksum
+    $HashFromDownload = Get-FileHash -Path $PythonInstallerPath -Algorithm MD5
+    if ($HashFromDownload.Hash -ne $PythonInstallerHash) {
+        throw "Invalid Python installer: failed checksum!"
+    }
+    Write-Host "Python installer $PythonInstallerPath validated."
+
+    # Installs Python
+    & $PythonInstallerPath /passive InstallAllUsers=1 PrependPath=1 Include_test=0 TargetDir=$PythonInstallPath
+    if (-Not $?) {
+        throw "The Python installation exited with error!"
+    }
+
+    # NOTE(lidiz) Even if the install command finishes in the script, that
+    # doesn't mean the Python installation is finished. If using "ps" to check
+    # for running processes, you might see ongoing installers at this point.
+    # So, we needs this "hack" to reliably validate that the Python binary is
+    # functioning properly.
+
+    # Wait for the installer process
+    Wait-Process -Name $PythonInstaller -Timeout 300
+    Write-Host "Installation process exits normally."
+
+    # Validate Python binary
+    $PythonBinary = "$PythonInstallPath\python.exe"
+    & $PythonBinary -c 'print(42)'
+    Write-Host "Python binary works properly."
+
+    # Installs pip
+    & $PythonBinary -m ensurepip --user
+
+    Write-Host "Python $PythonVersion installed by $PythonInstaller at $PythonInstallPath."
+}
+
+# Python 3.8
+$Python38x86Config = @{
+    PythonVersion = "3.8.0"
+    PythonInstaller = "python-3.8.0"
+    PythonInstallPath = "C:\python38_32bit"
+    PythonInstallerHash = "412a649d36626d33b8ca5593cf18318c"
+}
+Install-Python @Python38x86Config
+
+$Python38x64Config = @{
+    PythonVersion = "3.8.0"
+    PythonInstaller = "python-3.8.0-amd64"
+    PythonInstallPath = "C:\python38"
+    PythonInstallerHash = "29ea87f24c32f5e924b7d63f8a08ee8d"
+}
+Install-Python @Python38x64Config
+
+# Python 3.9
+$Python39x86Config = @{
+    PythonVersion = "3.9.0"
+    PythonInstaller = "python-3.9.0"
+    PythonInstallPath = "C:\python39_32bit"
+    PythonInstallerHash = "4a2812db8ab9f2e522c96c7728cfcccb"
+}
+Install-Python @Python39x86Config
+
+$Python39x64Config = @{
+    PythonVersion = "3.9.0"
+    PythonInstaller = "python-3.9.0-amd64"
+    PythonInstallPath = "C:\python39"
+    PythonInstallerHash = "b61a33dc28f13b561452f3089c87eb63"
+}
+Install-Python @Python39x64Config