Re: Frustrated with scopes

2009-08-12 Thread James Stroud 

James Stroud wrote:
 def stream_factory:
   class Line(object):
 __source = source
 __join = join
   # etc.
   return Line


of course I meant def stream_factory(lines, source, join=''.join):

James

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Re: Frustrated with scopes

2009-08-12 Thread Diez B. Roggisch 
andrew cooke wrote:

 On Aug 12, 7:49 am, andrew cooke and...@acooke.org wrote:
 On Aug 12, 1:51 am, James Stroud nospamjstroudmap...@mbi.ucla.edu
 wrote:



  andrew cooke wrote:
   Is there a way to make this work (currently scope and join are
   undefined at runtime when the inner class attributes are defined):

   class _StreamFactory(object):

   @staticmethod
   def __call__(lines, source, join=''.join):

   class Line(object):

   __source = source
   __join = join
   [...]

  It would be helpful if you were to describe the type of behavior you
  expect.

 Sorry, I didn't make myself clear.  When run the code gives
 NameError: name 'source' is not defined
 because the class namespace blocks the function namespace (or
 something...).
 
 ie when the __call__ method is invoked on an instance of
 _StreamFactory.

But you can refer to the arguments if you don't insist on setting them as
class-attributes:




def factory(foo, bar):

class A(object):

def do_something(self):
print foo, bar

return A()

a = factory(10, 20)
a.do_something()



Diez
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Re: Frustrated with scopes

2009-08-12 Thread Steven D'Aprano 
On Wed, 12 Aug 2009 04:49:06 -0700, andrew cooke wrote:

 It would be helpful if you were to describe the type of behavior you
 expect.
 
 Sorry, I didn't make myself clear.  When run the code gives
  NameError: name 'source' is not defined
 because the class namespace blocks the function namespace (or
 something...).

James asked you to describe the behaviour you expect. Please explain what 
you expect, and what you actually get. Post the ACTUAL error message, not 
a summary, not a paraphrase, but an actual copy and paste.


In any case, your code snippet works for me:


 class _StreamFactory(object):
... @staticmethod
... def __call__(lines, source, join=''.join):
... class Line(object):
... __source = source
... __join = join
...
 obj = _StreamFactory()
 obj(['a', 'b'], ab)


No errors. Of course it doesn't return anything, because your code 
snippet doesn't return anything either. Here's a modified version which 
returns the inner class:

 class _StreamFactory2(object):
... @staticmethod
... def __call__(lines, source, join=''.join):
... class Line(object):
... __source = source
... __join = join
... return Line
...
 obj = _StreamFactory2()
 K = obj(['a', 'b'], ab)
 K
class '__main__.Line'
 K._Line__source
'ab'


Works perfectly. I suspect your error is probably something like you have 
misspelled source somewhere.


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Steven
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Re: Frustrated with scopes

2009-08-12 Thread Dave Angel 

andrew cooke wrote:

Is there a way to make this work (currently scope and join are
undefined at runtime when the inner class attributes are defined):

class _StreamFactory(object):

@staticmethod
def __call__(lines, source, join=''.join):

class Line(object):

__source = source
__join = join
[...]

I can get something working by bouncing through global values, but it
looks awful and I think it's a source of a bug due too values being
redefined.

Thanks,
Andrew

  
Supply us with just enough source code to actually try it, give the full 
error message including traceback, and tell us what you expected to 
see.  Also tell us Python version   (sys.version)


So far you've done none of these.  When I try the following, I get no 
errors, using Python 2.6.2



class _StreamFactory(object):

   @staticmethod
   def __call__(lines, source, join=''.join):

   class Line(object):

   __source = source
   __join = join
   return Line()


fact = _StreamFactory()
obj = fact(43, name.txt)
print obj


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Re: Frustrated with scopes

2009-08-12 Thread andrew cooke 
On Aug 12, 8:52 am, Dave Angel da...@ieee.org wrote:
 Supply us with just enough source code to actually try it, give the full
 error message including traceback, and tell us what you expected to
 see.  Also tell us Python version   (sys.version)

 So far you've done none of these.  When I try the following, I get no
 errors, using Python 2.6.2

 class _StreamFactory(object):

     @staticmethod
     def __call__(lines, source, join=''.join):

         class Line(object):

             __source = source
             __join = join
         return Line()

 fact = _StreamFactory()
 obj = fact(43, name.txt)
 print obj

Ah!  OK, thanks for that.  I need to look at this again.  I'll post
again if necessary, but if it works for you then I clearly don't
understand what the issue is myself.

Andrew
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Frustrated with scopes

2009-08-11 Thread andrew cooke 

Is there a way to make this work (currently scope and join are
undefined at runtime when the inner class attributes are defined):

class _StreamFactory(object):

@staticmethod
def __call__(lines, source, join=''.join):

class Line(object):

__source = source
__join = join
[...]

I can get something working by bouncing through global values, but it
looks awful and I think it's a source of a bug due too values being
redefined.

Thanks,
Andrew
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Re: Frustrated with scopes

2009-08-11 Thread andrew cooke 
correction: source and join are undefined.  Sorry, Andrew

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Re: Frustrated with scopes

2009-08-11 Thread James Stroud 

andrew cooke wrote:

Is there a way to make this work (currently scope and join are
undefined at runtime when the inner class attributes are defined):

class _StreamFactory(object):

@staticmethod
def __call__(lines, source, join=''.join):

class Line(object):

__source = source
__join = join
[...]



It would be helpful if you were to describe the type of behavior you expect.

I assume you will return the newly created Line class when you call an 
instance of _StreamFactory? There may be some things about the above 
that you might be overlooking:


1. __call__ does not supersede the __init__ constructor of _StreamFactory.
2. __source and __join are name-mangled in later versions of python. 
They will be attributes of the returned Line class named _Line_source 
and _Line_join respectively.


Rather than make _StreamFactory a class, you will probably get the 
behavior you desire if you simply make it a function:


def stream_factory:
  class Line(object):
__source = source
__join = join
  # etc.
  return Line

And then don't forget that double underscores produce name mangling and 
you'll be set.


James


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