subclassing built-in types

From: Gabriel Cooper (gabriel.cooper_at_mediapulse.com)
Date: 05/24/04 

Date: Mon, 24 May 2004 17:08:19 -0400
To: python-list@python.org

I have data in lists of dictionaries with an accompanying array that I
would like to be able to treat as a normal array of strings so that it
will work with predefined functions that work with such, but I would
also like to have the ability to add and manipulate attributes, such as
each field's padding for output of the corresponding data:

(Running on RHFC2)

Python 2.3.3 (#1, May 7 2004, 10:31:40)
[GCC 3.3.3 20040412 (Red Hat Linux 3.3.3-7)] on linux2
[...]
IDLE 1.0.2
>>> class myString(str):
    def __init__(self, thestring, padding=0, *args,**kargs):
        str.__init__(self,thestring, *args,**kargs)
        self.padding = padding

       
>>> x = myString("hello")
>>> x
'hello'
>>> x.padding
0
>>> x = myString("hello",40)

Traceback (most recent call last):
  File "<pyshell#205>", line 1, in -toplevel-
    x = myString("hello",40)
TypeError: str() takes at most 1 argument (2 given)
>>> x = myString("hello")
>>> x.padding = 50
>>> x
'hello'
>>> x.padding
50
>>>

(in other words, I can do it in two steps, not one. I also tried
UserString and string as superclasses.)

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