How well do you know Python?

[Peter Otten]

Chris Angelico wrote:

> After some discussion with a Ruby on Rails programmer about where Ruby
> ends and where Rails begins (and it's definitely not where I'd have
> expected... Rails does a ton of monkey-patching, including of built-in
> types, to provide functionality that is strangely absent from the core
> language), I tried to come up with some somewhat-challenging Python
> questions. But to make them hard, I had to go a smidge more esoteric
> than the Ruby questions did.... Anyhow, see how you go. Assume Python
> 3.x unless stated.
> 
> 1) Under what circumstances can str.upper() return a string of
> different length to its input?
> 2) What exception do you get when you craft an impossible class hierarchy?
>     a. ValueError b. TypeError c. types.ClassInheritanceError d.
>     SyntaxError
> 3) What does `from __future__ import braces` do?
> 4) Which operator, removed from Python 3.0, can be reinstated with a
> 'joke' future directive?
> 5) What is the difference between the `/` and `//` operators in Python
> 2.7? In Python 3.x?
> 
> Got any other tricky questions to add?

What will 

$ cat foo.py 
import foo
class A: pass
print(isinstance(foo.A(), A))
$ python -c 'import foo'
...
$ python foo.py
...

print?

It looks like

$ python3 -c 'print({1, 2})'
{1, 2}
$ python3 -c 'print({2, 1})'
{1, 2}

will always print the same output. Can you construct a set from two small 
integers where this is not the case? What's the difference?

What happens if you replace the ints with strings? Why?