473,231 Members | 1,815 Online
Bytes | Software Development & Data Engineering Community
Post Job

Home Posts Topics Members FAQ

Join Bytes to post your question to a community of 473,231 software developers and data experts.

Can local function access local variables in main program?

I am confused by the following program:

def f():
print x
x=12345
f()

result is:
>>>
12345

however:
def f():
print x
x=0

x=12345
f()

result is:
Traceback (most recent call last):
File "...\test.py", line 5, in ?
f()
File "...\test.py", line 2, in f
print x
UnboundLocalError: local variable 'x' referenced before assignment
I am using
Python 2.4.4 (#71, Oct 18 2006, 08:34:43) [MSC v.1310 32 bit (Intel)]
on win32
I also tested it on python 2.5, which gives the same result.

Nov 3 '07 #1
8 3853
On Sat, 03 Nov 2007 07:18:17 +0000, Sullivan WxPyQtKinter wrote:
def f():
print x
x=0

x=12345
f()

result is:
Traceback (most recent call last):
File "...\test.py", line 5, in ?
f()
File "...\test.py", line 2, in f
print x
UnboundLocalError: local variable 'x' referenced before assignment

When Python compiles your function f(), it sees that you have assigned to
x, and that there is no line "global x", so it knows that x is a local
variable.

But when you call f(), you try to print x before the local x has a value
assigned to it. Hence the (accurate but hardly user-friendly) error
message.

You can also do this:
>>help(UnboundLocalError)
Help on class UnboundLocalError in module exceptions:

class UnboundLocalError(NameError)
| Local name referenced but not bound to a value.

As far as I know, there is no way to read the value of global x if and
only if local x doesn't exist.

--
Steven
Nov 3 '07 #2
On Sat, 03 Nov 2007 07:18:17 +0000, Sullivan WxPyQtKinter wrote:
I am confused by the following program:

def f():
print x
x=12345
f()

result is:
>>>>
12345
If python can't discover x in your current scope and you do not bind to
it there, it will automatically access that global name x.
however:
def f():
print x
x=0

x=12345
f()

result is:
Traceback (most recent call last):
File "...\test.py", line 5, in ?
f()
File "...\test.py", line 2, in f
print x
UnboundLocalError: local variable 'x' referenced before assignment
Here, you *do* assign to x in this scope so this is essentially the same
as the following (without any function scope)::

print x
x = 12345

This can't work since you haven't used x when you try to print it.

You can make this work using the `global` statement::
>>def foo():
... global x
... print x
... x = 0
...
>>x = 12345
print x
12345
>>foo()
12345
>>print x
0

See more in the `lexical reference about the global statement <http://
docs.python.org/ref/global.html>.

HTH,
Stargaming
Nov 3 '07 #3
Sullivan WxPyQtKinter wrote:
UnboundLocalError: local variable 'x' referenced before assignment
For your reference:

http://groups.google.de/groups?q=gro...oundLocalError

Regards,
Björn

--
BOFH excuse #12:

dry joints on cable plug

Nov 3 '07 #4
Actually I am quite satisfied with and error, which is my expectation.
But the implicit global variable access seems quite uncomfortable to
me. Why is that necessary?

On Nov 3, 3:39 am, Stargaming <stargam...@gmail.comwrote:
On Sat, 03 Nov 2007 07:18:17 +0000, Sullivan WxPyQtKinter wrote:
I am confused by the following program:
def f():
print x
x=12345
f()
result is:
12345

If python can't discover x in your current scope and you do not bind to
it there, it will automatically access that global name x.
Nov 3 '07 #5
Stargaming wrote:
You can make this work using the `global` statement::
>>def foo():
... global x
... print x
... x = 0
Is there any way to disable global for x? Something like that:
>>x = 12345
def foo():
.... global x
.... print x
.... noglobal(x) # ???
.... x = 0 # now this is local x
>>foo()
12345
>>print x
12345

--
In pariete - manus et crus cerebrumque

Nov 3 '07 #6
On Nov 3, 2007, at 5:32 PM, Pawel wrote:
Stargaming wrote:
>You can make this work using the `global` statement::
>>>>def foo():
... global x
... print x
... x = 0

Is there any way to disable global for x? Something like that:
>>>x = 12345
def foo():
... global x
... print x
... noglobal(x) # ???
... x = 0 # now this is local x
>>>foo()
12345
>>>print x
12345
Why would you need to do that? It would be confusing. Just use a
different variable name for the local.

Erik Jones

Software Developer | Emma®
er**@myemma.com
800.595.4401 or 615.292.5888
615.292.0777 (fax)

Emma helps organizations everywhere communicate & market in style.
Visit us online at http://www.myemma.com
Nov 3 '07 #7
Pawel wrote:
Is there any way to disable global for x? Something like that:
>>>x = 12345
def foo():
... global x
... print x
... noglobal(x) # ???
... x = 0 # now this is local x
Not really. Why don't you choose meaningful variable names? You
practically save nothing by using fewer names.

Regards,
Björn

--
BOFH excuse #423:

It's not RFC-822 compliant.

Nov 4 '07 #8
On 2007-11-03, Dennis Lee Bieber <wl*****@ix.netcom.comwrote:
On Sat, 03 Nov 2007 17:30:45 -0000, Sullivan WxPyQtKinter
<su***********@gmail.comdeclaimed the following in comp.lang.python:
>Actually I am quite satisfied with and error, which is my expectation.
But the implicit global variable access seems quite uncomfortable to
me. Why is that necessary?

Would you want to have to write things like:
Well it would be explicit and explicit is better than implicit.
import os
import os.path
import sys

def dFunc(more):
return "The full path of the item is: %s" % more

def aFunc(something):
global os.path
global sys
global dFunc
sys.stdout.write(dFunc(os.path.join("nonsense", something)))

Your "variable" follows the same logic used for name look ups of all
items -- "read" access will, after exhausting the local scope, search
the module level names (note that you don't need "global" to modify a
mutable object in module level -- it is only the rebinding of the name
itself that needs "global")
--
Antoon Pardon
Nov 8 '07 #9

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

15
by: John Doe | last post by:
Hi all, I know the standard doesn't care about threads (wrongly :-) But in current compilers implementation, is the "list" which holds count of the occupied and free heap addresses SHARED among...
12
by: Olumide | last post by:
I'm studying Nigel Chapman's Late Night Guide to C++ which I think is an absolutely fantastic book; however on page 175 (topic: operator overlaoding), there the following code snippet: inline...
2
by: Paul M | last post by:
Hi, This is on an AS/400 which can be a little strange but I think the basic question is portable. I have a (non-C) program that needs to make series of calls to some C programs/functions....
15
by: MackS | last post by:
The system I am working on supports a subset of C99, among which "standard-compliant VLAs". I've already learnt that VLAs can't have global scope. My question is whether I can safely declare a...
23
by: Timothy Madden | last post by:
Hello all. I program C++ since a lot of time now and I still don't know this simple thing: what's the problem with local functions so they are not part of C++ ? There surely are many people...
7
bvdet
by: bvdet | last post by:
I provide shop drawings to structural steel fabricators with SDS/2 software (http://sds2.com) by Design Data (DD). I am not a programmer by education or trade and started writing scripts about 5...
1
by: coolindienc | last post by:
I converted this program from using global variables to local variables. When I did that my while loop stopped working in my main function(module). Anyone, any idea why? I underlined the area where...
1
by: coolindienc | last post by:
I converted this program from using global variables to local variables. When I did that my while loop stopped working in my main function(module). Anyone, any idea why? I underlined the area where...
55
by: Zytan | last post by:
I see that static is more restricted in C# than in C++. It appears usable only on classes and methods, and data members, but cannot be created within a method itself. Surely this is possible in...
0
by: VivesProcSPL | last post by:
Obviously, one of the original purposes of SQL is to make data query processing easy. The language uses many English-like terms and syntax in an effort to make it easy to learn, particularly for...
0
by: jianzs | last post by:
Introduction Cloud-native applications are conventionally identified as those designed and nurtured on cloud infrastructure. Such applications, rooted in cloud technologies, skillfully benefit from...
0
by: abbasky | last post by:
### Vandf component communication method one: data sharing ​ Vandf components can achieve data exchange through data sharing, state sharing, events, and other methods. Vandf's data exchange method...
2
isladogs
by: isladogs | last post by:
The next Access Europe meeting will be on Wednesday 7 Feb 2024 starting at 18:00 UK time (6PM UTC) and finishing at about 19:30 (7.30PM). In this month's session, the creator of the excellent VBE...
0
by: fareedcanada | last post by:
Hello I am trying to split number on their count. suppose i have 121314151617 (12cnt) then number should be split like 12,13,14,15,16,17 and if 11314151617 (11cnt) then should be split like...
1
by: davi5007 | last post by:
Hi, Basically, I am trying to automate a field named TraceabilityNo into a web page from an access form. I've got the serial held in the variable strSearchString. How can I get this into the...
0
by: DolphinDB | last post by:
The formulas of 101 quantitative trading alphas used by WorldQuant were presented in the paper 101 Formulaic Alphas. However, some formulas are complex, leading to challenges in calculation. Take...
0
by: Aftab Ahmad | last post by:
Hello Experts! I have written a code in MS Access for a cmd called "WhatsApp Message" to open WhatsApp using that very code but the problem is that it gives a popup message everytime I clicked on...
0
by: Aftab Ahmad | last post by:
So, I have written a code for a cmd called "Send WhatsApp Message" to open and send WhatsApp messaage. The code is given below. Dim IE As Object Set IE =...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.