> 1 the next code SHOULD produce an error message. Think that it's followed
> by a few dozens of code lines:
> from turtle import *
> fd; rt(90)

There's no reasonable mechanism in current Python by which this could produce an error message; it's not an error, and you'd need to make substantial changes to the core language to make it such, including fleshing out exactly what those changes would be and how they'd work, and persuading other core developers that those changes improve the language.

As Nick Timkovich points out, tools like pylint will flag this sort of thing. When I run pylint on your script, the output includes the following:

> untitled.py:3:8: W0104: Statement seems to have no effect (pointless-statement) 

If you really want to pursue the necessary changes in the core language, I'd suggest starting a discussion on the python-ideas mailing list; others may have innovative suggestions for ameliorating the core problem. But it's just not feasible in the language as it stands.

I'd suggest focusing this issue on your second item, and dropping the first.