Neither in Perl. Because there are no variable markers in Python, there are no variable interpolation in strings. A function that returns a list must be coerced into a tuple to use this, though. Often Python's error messages leave something to be desired. This is also true in slices, which is the real gotcha part.
Negative subscripts count back from the right.
Same as in Perl. Slices can omit either the starting point or the ending point. Python doesn't convert between strings and numbers unless you tell it to. And if you don't tell it to, you get an exception. The first would concat strings or lists, the last would repeat them.