[Edu-sig] this is interesting

[michel paul]

>> def f(n, history = []):
  history.append(n)
  return history

>>> f(1)
[1]
>>> f(2)
[1, 2]
>>> f(3)
[1, 2, 3]
>>> f(2)
[1, 2, 3, 2]
>>> f(1)
[1, 2, 3, 2, 1]
>>> f(1,[])
[1]

A student wrote me wondering why his function wouldn't 'clear' after being
called.  He meant to create an empty list and ended up with something like
this.

What's a good way to explain what's going on?

- Michel



-- 
==================================
"What I cannot create, I do not understand."

- Richard Feynman
==================================
"Computer science is the new mathematics."

- Dr. Christos Papadimitriou
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