Shell and Python3?

Executing “python --version” and “python3 --version” in a MacOS terminal both show me correct results.
In my program I run a shell to execute python scripts. The shell command “python --version” shows me the correct result as well, but the shell command “python3 --version” gives me the error “bash: python3: command not found”.
Does anyone know why?

mac OS version ?

MacOS version 10.14.3
Python version 2.7.10
Python3 version 3.7.1

You need to add the location of your Python installation for the Xojo shell. Shell ain’t bash.

That worked. Thank you very much!