[Tutor] lists of lists: more Chutes & Ladders!

[Mark Lawrence]

On 31/12/2013 07:30, Keith Winston wrote:
> Never mind, I figured out that the slice assignment is emptying the
> previous lists, before the .reset() statements are creating new lists
> that I then populate and pass on. It makes sense.
>
> On Tue, Dec 31, 2013 at 12:59 AM, Keith Winston <keithwins at gmail.com
> <mailto:keithwins at gmail.com>> wrote:
>
>     I resolved a problem I was having with lists, but I don't understand
>     how! I caught my code inadvertently resetting/zeroing two lists
>     TWICE at the invocation of the game method, and it was leading to
>     all the (gamechutes & gameladders) lists returned by that method
>     being zeroed out except the final time the method is called. That
>     is: the game method below is iterated iter times (this happens
>     outside the method), and every time gamechutes and gameladders
>     (which should be lists of all the chutes and ladders landed on
>     during the game) were returned empty, except for the last time, in
>     which case they were correct. I can see that doing the multiple
>     zeroing is pointless, but I can't understand why it would have any
>     effect on the returned values. Note that self.reset() is called in
>     __init__, so the lists exist before this method is ever called, if I
>     understand properly.
>
>          def game(self, iter):
>              """Single game"""
>
>              self.gamechutes[:] = []   #when I take out these two slice
>     assignments,
>              self.gameladders[:] = []   # then gamechutes & gameladders
>     work properly
>
>              self.gamechutes = []  # these were actually in a call to
>     self.reset()
>              self.gameladders = []
>
>              #.... other stuff in reset()
>
>              while self.position < 100:
>                  gamecandl = self.move()
>                  if gamecandl[0] != 0:
>                      self.gamechutes.append(gamecandl[0])
>                  if gamecandl[1] != 0:
>                      self.gameladders.append(gamecandl[1])
>              return [iter, self.movecount, self.numchutes,
>     self.numladders, self.gamechutes,            self.gameladders]
>
>     I'm happy to share the rest of the code if you want it, though I'm
>     pretty sure the problem lies here. If it's not obvious, I'm setting
>     myself up to analyse chute & ladder frequency: how often, in a
>     sequence of games, one hits specific chutes & ladders, and related
>     stats.
>
>     As always, any comments on style or substance are appreciated.
>

Please intersperse or bottom post, top posting makes things very 
difficult to follow, especially in long threads.

TIA.

-- 
My fellow Pythonistas, ask not what our language can do for you, ask 
what you can do for our language.

Mark Lawrence