Newbie question: unexpected diagnostic when subclassing

[Chris Liechti]

"Jeff Melvaine" <jeffm52 at rivernet.com.au> wrote in 
news:3d472b34$1 at news.rivernet.com.au:

> I think I must be doing something basically wrong, but ... ???
> 
> I'm running Python 2.1 on Windows 98.  I create a file x.py in which I
> declare
> 
> class x:
>   ...
> 
> The basic operations of this class work OK.
> 
> I then create a file y.py in which I declare
> 
> class y(x):
>   ...

thats a confusing naming scheme.. usual are words starting with a capital 
letter for class names.

> When I try to create an instance of y, I get the diagnostic
> 
> TypeError: base is not a class instance
> 
> referenced to the definition of class y.  In this context, does x really
> have to be a variable whose value is an instance of class x?

no it should be a class or type (on 2.2).

class A:
  """base class"""

class B(A):
  """subclassing from A"""

b = B()    	#instantiate B

if you place them in separate files, you have to import it:

import a    	#load a.py
class B(a.A):
    	...

if you use python 2.2, taking built in types as base class it works too 
(well type names are all lower case, but still name the user class with 
capitals):

class MyFancyList(list):
    	def append(self, item):
    	    	"""a stringifying append"""
    	    	list.append(self, str(item))
    	def toString(self, delim = ''):
    	    	"""make a string out of it"""
    	    	return delim.join(self)

ml = MyFancyList()
ml.append("hello")
ml.append(1)
ml.append(2)
ml.append(3)
print ml.toString()


chris

-- 
Chris <cliechti at gmx.net>