Scope problem with nested functions.

[AddisonN]

I'm having trouble resolving a 
scope problem. I have a module, called from another script, with this 
structure:
 
def parseFile(file, myLocation, 
defaults):
 # 
initialisation.
 
ccyMappings = {}
 
 def 
getCcyMappings()
  global 
ccyMappings
  # read values into 
ccyMappings.
  ccyMappings['CAN'] 
= ['CAD'] # for example.
 
    def mapCcy(myCcy):    if 
ccyMappings.has_key(myCcy):    
return ccyMapping['myCcy']    
else:    return myCcy   
 
 
My problem is that, although 
the ccyMappings dictionary is populated within the def getCcyMappings() 
function, the value goes to 'None' when I leave it and so is not available when 
the mapCcy function is called. I've used the global scope declaration 
successfully before, but not with nested functions like this, 
admittedly.
 
Any assistance gratefully 
received.
 
Nick.
 
 
 

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RE: Scope problem with nested functions.

[AddisonN]

Thanks Fredrik, that's fixed it. Apologies for the lazy typing - should
have cut and pasted the whole thing.

-Original Message-
From: Fredrik Lundh [mailto:[EMAIL PROTECTED] 
Sent: 13 October 2005 08:55
To: python-list@python.org
Subject: Re: Scope problem with nested functions.

<[EMAIL PROTECTED]> wrote

> I'm having trouble resolving a scope problem. I have a module, called 
> from another script, with this structure:

the code you posted gives a syntax error.  if I fix that, and add some
boilerplate to call getCcyMappings from inside the parseFile function, I
get:

Traceback (most recent call last):
  File "script.py", line 19, in ?
parseFile(0, 0, 0)
  File "script.py", line 17, in parseFile
getCcyMappings()
  File "script.py", line 8, in getCcyMappings
ccyMappings['CAN'] = ['CAD'] # for example.
NameError: global name 'ccyMappings' is not defined

which tells you that there is no *global* variable named ccyMappings.

the ccyMappings variable in your example isn't a global variable; it's
local to the parseFile function, and can be accessed from that function
and any inner functions via normal lexical scoping rules (=access, but
not rebind).

however, the global statement tells Python that the given name is a
global variable, and that any attempts to access or rebind that variable
should be done at the global (=module) level.

if you remove the global statement, Python will look for variables using
ordinary lexical scoping, and things will work as expected.

 






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