scope of variables

[Gary Wessle]

Hi

is the code below correct?

b = 3
def adding(a)
print a + b

it seams not to see the up-level scope where b is defined.

thanks

[Marc 'BlackJack' Rintsch]

Re: scope of variables

In <874q06bz4c.fsf @localhost.loca ldomain>, Gary Wessle wrote:
[color=blue]
> is the code below correct?[/color]

No...
[color=blue]
> b = 3
> def adding(a)[/color]

....a colon is missing at the end of the above line.
[color=blue]
> print a + b
>
> it seams not to see the up-level scope where b is defined.[/color]

It does. And you could easily find out yourself by just trying that code.
Running this::

b = 3
def adding(a):
print a + b

adding(5)

Puts out 8 as expected.

Ciao,
Marc 'BlackJack' Rintsch

[Steve R. Hastings]

Re: scope of variables

On Thu, 04 May 2006 07:02:43 +1000, Gary Wessle wrote:[color=blue]
> b = 3
> def adding(a)
> print a + b
>
> it seams not to see the up-level scope where b is defined.[/color]

Assuming you put a ':' after the "def adding(a)", this should work in
recent versions of Python. In Python 2.0 and older, this will not work.


In Python 2.1, it will only work if you do this:

from __future__ import nested_scopes


When you first start Python interactively, it should print version
information. Here's what my Python prints when I start it:

Python 2.4.3 (#2, Apr 27 2006, 14:43:58)
[GCC 4.0.3 (Ubuntu 4.0.3-1ubuntu5)] on linux2
Type "help", "copyright" , "credits" or "license" for more information.


As you can see, I'm running Python 2.4.3. Make sure you aren't running an
old version of Python, and that code should do what you expect.
--
Steve R. Hastings "Vita est"
steve@hastings. org http://www.blarg.net/~steveha

[Ben Finney]

Re: scope of variables

Gary Wessle <phddas@yahoo.c om> writes:
[color=blue]
> is the code below correct?[/color]

It's best to post an example that you've tried yourself, and that is
small but completely demonstrates the issue in question.
[color=blue]
> b = 3
> def adding(a)
> print a + b[/color]

This, for example, would fail the syntax check (the 'def' statement
needs a trailing colon). After that's fixed, the code runs, but shows
no output.

A complete, minimal, working example will help people answer your
question.

--
\ "[W]e are still the first generation of users, and for all that |
`\ we may have invented the net, we still don't really get it." |
_o__) -- Douglas Adams |
Ben Finney

[Gary Wessle]

Re: scope of variables

"Steve R. Hastings" <steve@hastings .org> writes:
[color=blue]
> On Thu, 04 May 2006 07:02:43 +1000, Gary Wessle wrote:[color=green]
> > b = 3
> > def adding(a)
> > print a + b
> >
> > it seams not to see the up-level scope where b is defined.[/color]
>
> Assuming you put a ':' after the "def adding(a)", this should work in
> recent versions of Python. In Python 2.0 and older, this will not work.[/color]

the example was an in-accuretlly representation of a the problem I am
having. my apologies.

a = []
def prnt():
print len(a)
[color=blue][color=green][color=darkred]
>>> prnt[/color][/color][/color]
<function prnt at 0xb7dc21b4>

I expect to get 0 "the length of list a"

[Leif K-Brooks]

Re: scope of variables

Gary Wessle wrote:[color=blue]
> the example was an in-accuretlly representation of a the problem I am
> having. my apologies.
>
> a = []
> def prnt():
> print len(a)
>[color=green][color=darkred]
>>>> prnt[/color][/color]
> <function prnt at 0xb7dc21b4>
>
> I expect to get 0 "the length of list a"[/color]

Python requires parenthesis to call a function.
[color=blue][color=green][color=darkred]
>>> a = []
>>> def prnt():[/color][/color][/color]
... print len(a)
...[color=blue][color=green][color=darkred]
>>> prnt[/color][/color][/color]
<function prnt at 0xb7dcad84>[color=blue][color=green][color=darkred]
>>> prnt()[/color][/color][/color]
0

[Lord Landon]

Re: scope of variables

Try >>> prnt()
o.o'

On 04 May 2006 08:25:01 +1000, Gary Wessle <phddas@yahoo.c om> wrote:[color=blue]
> "Steve R. Hastings" <steve@hastings .org> writes:
>[color=green]
> > On Thu, 04 May 2006 07:02:43 +1000, Gary Wessle wrote:[color=darkred]
> > > b = 3
> > > def adding(a)
> > > print a + b
> > >
> > > it seams not to see the up-level scope where b is defined.[/color]
> >
> > Assuming you put a ':' after the "def adding(a)", this should work in
> > recent versions of Python. In Python 2.0 and older, this will not work..[/color]
>
> the example was an in-accuretlly representation of a the problem I am
> having. my apologies.
>
> a = []
> def prnt():
> print len(a)
>[color=green][color=darkred]
> >>> prnt[/color][/color]
> <function prnt at 0xb7dc21b4>
>
> I expect to get 0 "the length of list a"
> --
> http://mail.python.org/mailman/listinfo/python-list
>[/color]


--
Lord Landon rules over all!

[Ryan Forsythe]

Re: scope of variables

Gary Wessle wrote:[color=blue]
> the example was an in-accuretlly representation of a the problem I am
> having. my apologies.
>
> a = []
> def prnt():
> print len(a)
>[color=green][color=darkred]
>>>> prnt[/color][/color]
> <function prnt at 0xb7dc21b4>
>
> I expect to get 0 "the length of list a"[/color]

You want prnt(), not prnt:
[color=blue][color=green][color=darkred]
>>> a = []
>>> def prnt():[/color][/color][/color]
.... print len(a)
....[color=blue][color=green][color=darkred]
>>> prnt[/color][/color][/color]
<function prnt at 0x43c70>[color=blue][color=green][color=darkred]
>>> prnt()[/color][/color][/color]
0

--Ryan

[Rob E]

Re: scope of variables

> is the code below correct?[color=blue]
>
> b = 3
> def adding(a)
> print a + b
>
> it seams not to see the up-level scope where b is defined.[/color]

Yes except for the missing : at the end of the "def" line.

Rob

[Gary Wessle]

Re: scope of variables

Ryan Forsythe <ryan@cs.uorego n.edu> writes:
[color=blue]
> Gary Wessle wrote:[color=green]
> > the example was an in-accuretlly representation of a the problem I am
> > having. my apologies.
> >
> > a = []
> > def prnt():
> > print len(a)
> >[color=darkred]
> >>>> prnt[/color]
> > <function prnt at 0xb7dc21b4>
> >
> > I expect to get 0 "the length of list a"[/color]
>
> You want prnt(), not prnt:
>[/color]

I finally was able to duplicate the error with a through away code
as follows,

*************** *************** *************** *************** ****
acc = [1,2,3]

def a():
b = [4, 5, 6]
acc = acc + b
print len(acc)

a()

*************** * error *************** *
Traceback (most recent call last):
File "a.py", line 12, in ?
a()
File "a.py", line 9, in a
acc = acc + b
UnboundLocalErr or: local variable 'acc' referenced before assignment

[bruno at modulix]

Re: scope of variables

Gary Wessle wrote:[color=blue]
> Ryan Forsythe <ryan@cs.uorego n.edu> writes:
>
>[color=green]
>>Gary Wessle wrote:
>>[color=darkred]
>>>the example was an in-accuretlly representation of a the problem I am
>>>having. my apologies.
>>>[/color][/color][/color]
(snip)[color=blue]
> I finally was able to duplicate the error with a through away code
> as follows,
>
> *************** *************** *************** *************** ****
> acc = [1,2,3]
>
> def a():
> b = [4, 5, 6]
> acc = acc + b
> print len(acc)
>
> a()
>
> *************** * error *************** *
> Traceback (most recent call last):
> File "a.py", line 12, in ?
> a()
> File "a.py", line 9, in a
> acc = acc + b
> UnboundLocalErr or: local variable 'acc' referenced before assignment[/color]

This is a FAQ:

http://www.python.org/doc/faq/programming/#what-are-the-rules-for-local-and-global-variables-in-python

For short: if a name is 'assigned' (in Python, the correct term is
'bound') in the local scope, it'll be considered a local name. If it's
*only* accessed, it'll be looked up in the enclosing namespace - here
the so-called 'global' (which means: 'module') namespace.

The dirty solution is to declare 'acc' as global in the function:
def a():
b = [4, 5, 6]
global acc
acc = acc + b
print len(acc)

but this is really BadCode(tm). As a general rule, functions should not
silently modify or rebind global variables - this leads to maintenance
nightmares. In this case, you should manage to either 1/ pass acc as a
param to a(), or 2/ have a() return the sequence to be added to acc:

# 1
acc = [1,2,3]
def a(alist):
alist.extend([4, 5, 6])
return alist

acc = a(acc)
print acc, len(acc)

# 2
acc = [1,2,3]
def a():
return [4, 5, 6]

acc.extend(a())
print acc, len(acc)


The Right Thing(tm) to do of course depends on the real code, so it may
be yet another solution, but it's impossible to decide with dummy code...

--
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb@xiludom. gro'.split('@')])"

[Gary Wessle]

Re: scope of variables

thank you