Here's my advice about the most important thing Python does:

    >>> if x = y:
      File "<stdin>", line 1
        if x = y:
             ^
    SyntaxError: invalid syntax

Why is this important? Because it's such a damnably subtle bug. But what if people want to do something like if r = get_result(): r.do_something()? Make them write if r with r as get_result(): r.do_something() instead.