+1 for this. As a side effect, it replaces the ns parameter which I found not really explicit.

avoid pollution of global namespace

Can you add some tests that demonstrate this please?

Can you add some tests that demonstrate this please?

Of course =)

@casatir How's that look for a test?

I also changed mode ==> return_mode (more explicit) and changed it so that it will raise an error if passed an unexpected mode. Otherwise it's way too easy for someone to pass i.e., "last-expr-or-assign" or "last_exp_or_assign" and be confused when it does something different than expected. It could be friendly to offer:

class ReturnMode:
    LAST_EXPR = "last_expr"
    LAST_EXPR_OR_ASSIGN = "last_expr_or_assign"
    NONE = None

which would make Jedi more helpful for instance.