1 Go to Control Panel, System, Advanced System Settings, Environmental Variables.
2 Edit the User and System Variables of PATH, delete both python values C:\Python27 and C:\Python27\Scripts
3 Add to PATH the variables %PYTHON_HOME% and %PYTHON_HOME%\Scripts
4 Now make a new Environmental Variable named PYTHON_HOME with the value C:\Python27
Until Command Prompt is closed we can now temporarily change the Python version from Python2.7 to Python3.7 with the following:
set PYTHON_HOME=C:\Python37
set PATH=%PYTHON_HOME%;%PYTHON_HOME%\Scripts;%PATH%
You can also save the following as py37.bat and run it in CMD
@echo off
echo setting PYTHON_HOME = C:\Python37
set PYTHON_HOME=C:\Python37
echo setting PATH = %PYTHON_HOME%;%PYTHON_HOME%\Scripts;
set PATH=%PYTHON_HOME%;%PYTHON_HOME%\Scripts;%PATH%