See the below GIF

How does the documentation for all the functions appear as you type in the terminal?
I am already familiar with autocompletion and there are bunch to tutorials to do this but what about function definition? Currently I am using pip install ptpython module to get autocompletion feature but I want to know the function definition as well. Could anyone help me?
Got my answer from @Padraic Cunningham. See the comment section.
This is a bpython shell. You can download using
piporapt-get install bpythonTo start go to your terminal and type
bpython