[Tutor] Globals?

[Lloyd Kvam]

But integers are immutable.

If names could be rebound as a side-effect of a function call, you would
be creating some difficult to debug connections in your program.  

If you are deliberately creating a special environment for communicating
between functions sharing that environment (closures), it probably makes
sense to use a dictionary or class to separate those variable names from
the "general" variables.  A list works, since it is mutable.

I guess I'm not a closure purist.

On Sat, 2004-11-13 at 15:57, Kent Johnson wrote:
> I think the idea is that x in the enclosing scope should be changed when 
> _ is called. To closure purists :-) a language doesn't have closures if 
> it can't do this.
> 
> Python will bind the *values* of variables in an enclosing scope into a 
> closure, which is good enough for many uses :-)
> 
> Personally I haven't found much need for 'true' closures. orbitz, can 
> you say why this is such a pain? How would you use a true closure?
> 
> A workaround is to store the variable in a list, but it's a bit ugly:
> 
> x = [3]
> def fn(x):
>      def _():
>         x[0] += 1
>         return x[0]
>      return _
> 
> Kent
> 
> Lloyd Kvam wrote:
> > It DOES work in current versions of Python, exactly as you coded it.
> > 
> > In older Pythons (e.g. 1.52) you would have had to specifying the
> > enclosing variables explicitly
> > 	def _(x=x):
> > 
> > A lot of old critiques are still present on the web.  wikipedia has a
> > terrific article describing Python that is current (at least 2.3.3).
> > 
> > http://en.wikipedia.org/wiki/Python_programming_language
> > 
> > 
> > 
> > On Sat, 2004-11-13 at 14:07, orbitz wrote:
> > 
> >>In my opinion, this behavior really sucks too. Like when it comes to 
> >>closures.  As far as I know, Python does not *really* support closures, 
> >>like you would get with something like lisp. Correct me if I'm wrong.  
> >>This means code like:
> >>
> >>def fn(x):
> >>    def _():
> >>       x += 1
> >>       return x
> >>    return _
> >>
> >>Will not work, which can be a pain in the ass.
> >>
> >>
> >>Kent Johnson wrote:
> >>
> >>
> >>>Liam,
> >>>
> >>>When you make any assignment to a variable inside a function, Python 
> >>>assumes that the variable is local to the function. Then any use of 
> >>>the variable before it's first assignment is an error.
> >>>
> >>>To force a variable in a function to be global, put a 'global' 
> >>>statement in the function. You need to add
> >>>  global badConnectCycle
> >>>to your function getReturns
> >>>
> >>>If you don't make any assignment to a variable, then the global 
> >>>(module) namespace is searched. That is why badUserList works fine - 
> >>>you never assign it, you just access the list methods.
> >>>
> >>>Kent
> >>>
> >>>Liam Clarke wrote:
> >>>
> >>>
> >>>>Hi all,
> >>>>Having trouble with something, it is 3:30am in the morning, so this
> >>>>may be a dumb problem, if so, I apologise.
> >>>>
> >>>>In my prog, there's two variables created right at the get go -
> >>>>
> >>>>import imaplib
> >>>>import email.Parser
> >>>>import os
> >>>>import os.path
> >>>>import datetime
> >>>>import md5
> >>>>from pause import *
> >>>>
> >>>>badUserList=[]
> >>>>badConnectCycle=0
> >>>>
> >>>>as I want them to be global within this module, so that another module
> >>>>can pick them out easily.
> >>>>
> >>>>Now, I just added badConnectCycle, badUserList has been there awhile,
> >>>>and it's used in
> >>>>
> >>>>the function connectToImap which is called by getReturns which is
> >>>>called by main(), and my other module can get it no problem, so
> >>>>badUserList is fine.
> >>>>
> >>>>badConnectCycle... is giving me errors -
> >>>>
> >>>>badConnectCycle is used in getReturns, as so -
> >>>>if session == "NoConnect" :             badConnectCycle += 1
> >>>>            continue
> >>>>
> >>>>
> >>>>function getReturns ends as follows -
> >>>>if badConnectCycle == len(user) and badConnectCycle > 0: return 
> >>>>("NoConnect","")
> >>>>if badUserList and not sender: return ('NoLogin',"")
> >>>>if matchindex[0] and not sender: return ('NoNew', '')
> >>>>if not sender: return ("NoMatch","")
> >>>>return (sender, msgdata)
> >>>>
> >>>>and it's at that line
> >>>>
> >>>> if badConnectCycle == len(user) and badConnectCycle > 0:
> >>>>
> >>>>that I get this error:
> >>>>
> >>>>UnboundLocalError: local variable 'badConnectCycle' referenced before
> >>>>assignment.
> >>>>
> >>>>Which is confusing me because badUserList is used within a function
> >>>>called by getReturns, and I've had no problem with it.
> >>>>
> >>>>Help anyone? Much appreciated if you can.
> >>>>
> >>>>Regards,
> >>>>
> >>>>Liam Clarke
> >>>
> >>>_______________________________________________
> >>>Tutor maillist  -  Tutor at python.org
> >>>http://mail.python.org/mailman/listinfo/tutor
> >>>
> >>
> >>_______________________________________________
> >>Tutor maillist  -  Tutor at python.org
> >>http://mail.python.org/mailman/listinfo/tutor
> _______________________________________________
> Tutor maillist  -  Tutor at python.org
> http://mail.python.org/mailman/listinfo/tutor
-- 
Lloyd Kvam
Venix Corp