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.johans...@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....@gmail.com] > Skickat: den 30 maj 2010 18:34 > Till: Robert Johansson > Kopia: tutor@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 > > > _______________________________________________ > Tutor maillist - Tutor@python.org > To unsubscribe or change subscription options: > http://mail.python.org/mailman/listinfo/tutor >
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