TypeError, I know why but not how!?

[Robert Kern]

ssecorp wrote:
> Im looking into PvsNP:
> http://www.claymath.org/millennium/P_vs_NP/
> so I thought I'd write the program just to get a feel for it.
> 
> 
> But I run into a problem. Why does it all the sudden return None? I
> mean I know why the program aborts but I dont understand why the None
> is generated all the sudden. Hitting recursion depth isn't reported
> with that error.

def validate(placed):
     student = round(random.random()*401)
     if student in placed:
         # You need to explicitly return, here:
         return validate(placed)
     else:
         placed.append(student)
         return student, placed

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco