[Tutor] namespaces

[Matthew Wood]

That's probably my least favorite error message in python.  I wish that
somehow it would have the line number of the first assignment statement
instead of the first read statement.  I know why it's not that way, but I
just wish it weren't.

--

I enjoy haiku
but sometimes they don't make sense;
refrigerator?


On Sun, May 30, 2010 at 10:47 AM, Robert Johansson <
robert.johansson at math.umu.se> wrote:

> Thanks Evert for pointing out the difference and the discussion on global
> variables, it helped.
>
> /Robert
>
> -----Ursprungligt meddelande-----
> Från: Evert Rol [mailto:evert.rol at gmail.com]
> Skickat: den 30 maj 2010 18:34
> Till: Robert Johansson
> Kopia: tutor at python.org
> Ämne: Re: [Tutor] namespaces
>
>  Hi Robert
>
> > This code generates the message "UnboundLocalError: local variable
> 'doubles' referenced before assignment" (line: if d[0] == d[1] and doubles
> == 2:)
> >
> > http://pastebin.com/mYBaCfj1
> >
> > I think I have a fair picture of what it means but I would be very happy
> if someone could explain the difference between the two variables h and
> doubles in the code. Why is one accessible from the function but not the
> other? I looked into rules for namespaces but I'm still confused. Below is
> another sample of the code
>
> You assign a value to doubles in the roll() function, making Python think
> doubles is a local variable (which hasn't been assigned anything when you
> first use it, throwing the exception).
> If you assign some value to h after the first line in roll() (eg, h = 6),
> you'd get the same exception, but then for h.
> So, if you assign a value to a variable inside a function() and you want
> that variable to be the global one (instead of the implicitly assumed local
> one), you'll have to explicitly tell Python that: "global doubles" (probably
> on the first line in the function).
> Since you hadn't assigned any value to h inside roll(), only used it,
> Python assumes it's the global one.
>
> See also the second answer to this question:
> http://stackoverflow.com/questions/423379/global-variables-in-python
>
> Hope that helps,
>
>  Evert
>
>
> >
> > Cheers, Robert
> >
> > from random import *
> >
> > h = 6
> > doubles = 0 # current number of consecutive doubles
> >
> > def roll():
> >     d = [randint(1, h), randint(1, h)]
> >     if d[0] == d[1] and doubles == 2:
> >         doubles = 0
> >         return 0
> >     elif d[0] == d[1] and doubles < 2:
> >         doubles += 1
> >         return sum(d)
> >     else:
> >         return sum(d)
> >
> > for n in range(10):
> >     d = roll()
> >     print d
> >
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