How does one view the source of function defined in the interpreter?

[Terry Reedy]

mattc wrote:
Once the interpreter reads lines of code, then, as far as the 
interpreter is concerned, they are gone.

> 3) One last thing, is there any documentation for augmenting,
> extending, or editing a function in the interpreter once it is
> defined?

Use IDLE, edit code in an edit window, then run.
I generally use the interpreter or IDLE shell window only for 
single-line commands.