Installing Python 3 on Windows.
Step 1. Download the latest version of Python 3.6 from the official website.
https://www.python.org/downloads/
Step 2. Add the directory C:\Python36\ for your default Python version to the PATH.
PATH:
C:\Python36\;C:\Python36\Scripts\
You can do this easily by running the following in powershell:
[Environment]::SetEnvironmentVariable("Path", "$env:Path;C:\Python36\;C:\Python36\Scripts\", "User")
another variation
[Environment]::SetEnvironmentVariable("Path", "$env:Path;C:\Python36")
or
[System.Environment]::SetEnvironmentVariable("PATH", $Env:Path + ";C:\Python36", "Machine")
Step 3. Please restart the Powershell after that.