As you install Python, simply be sure to tick the box that says “Add Python to PATH.” This can be found at the bottom of the image and it may be unticked by default! How to add Python manually ...

Your Python development setup is incomplete if you don't add it to the system’s PATH. Doing so saves time and effort and ...

Python scripts that begin with a line in the format of #!/path/to/python python3 or #!"C:Python3.3python.exe" will be run with the interpreter specified there.