Help needed - function apparently global cannot be called.

Tue Sep 7 06:50:19 EDT 2010

Ian Hobson a écrit :
> Hi all you experts,
>> This has me beat. Has anyone any ideas about what might be going wrong?
>> This is code from within a windows service (hence no print statements - 
> no sys.stdout to print on!).
>> I am trying to trace through to find where the code is not working. No 
> stdout so I have to log to a file.

Then you'd be better using the logging module from the stdlib. And FWIW, 
 you should try to make you code testable in a non-service context...
> I have the following code fragments.
>> def log(message):
> f = open('d:\logfile.txt','a')
> f.write(message + "\n")
> f.close()
>> from DelNotePrinter import DelNotePrinter

<OT>
The convention is to use all_lower_names for modules - having modules 
and classes with the same (case-sensitive) name can be very misleading.
</OT>
> note the order of the above - log is defined before the import.

And ? Do you think it will affect the imported module in any way ? Like, 
say, magically "inject" your log function in the DelNotePrinter module ?-)
> Later in the source

Where ?
> I have
>> log('disPrint is:'+disPrint)
> log('count is:'+count)

Do yourself a favor and learn string formating...
> log(repr(DelNotePrinter))
> printer = DelNotePrinter(disPrint,int(count))

> The DelNotePrinter.py file cannot us log even though it is declared
> as global.

In Python, "global" means "module-level", and it's only necessary when 
you want to rebind a module-level name from within a function or method.
 The code is...
>> # coding=utf8
> # DelNotePrinter = code to print delivery notes
> assorted imports removed for space reasons

Some of these imports surely explain why you don't just get a NameError 
when trying to call log() - wild guess : you have some "from xxx import 
*" statement that does import another callable named 'log'.
> class DelNotePrinter(object):
> ''' Print Delivery Note on A5 in portrait '''
> def __init__(self,printer,copies):
> ''' create printer and painter '''
> global font,sm,log
> log('DelNotePrinter: starting')

> self.printer = QPrinter(QPrinter.HighResolution)

If you want to access a name (function, class, whatever) defined in 
another module, you have to explicitely import it.
>> The file the log writes contains..
> disPrint is:HP Deskjet 6940 series
> count is:1
> <class 'DelNotePrinter.DelNotePrinter'>
>> The > is followed by a newline and end of file! Where is the 
> DelNotePrinter: starting message?

We can't tell - but you can get at least some hint, cf below
> If I replace the opening of __init__ with
> global font,sm,log
> f = open('d:\logfile.txt','a')
> f.write('DelNotePrinter: starting' + "\n")
> f.close()
> self.printer = QPrinter(QPrinter.HighResolution)
>> then the message IS written to the log file.

Obviously, yes. Now please add this to your code:
class DelNotePrinter(object):
 ''' Print Delivery Note on A5 in portrait '''
 def __init__(self,printer,copies):
 ''' create printer and painter '''
 global font,sm,log
 f = open('d:\logfile.txt','a')
 f.write('DelNotePrinter: starting' + "\n")
 # check what "log" is bound to in the currrent namespace
 f.write(
 "DelNotePrinter : log is '%s' from '%s'" % (
 log, log.__module__
 ))
 f.close()
 self.printer = QPrinter(QPrinter.HighResolution)
> I have read http://docs.python.org/reference/simple_stmts.html#global 
> very carefully and I still don't understand.

The statement definition makes no sense if you don't understand 
namespaces and bindings:
http://docs.python.org/reference/executionmodel.html#naming-and-binding