Subclassing array.array

Peter Otten __peter__ at web.de
Fri Jun 18 18:38:01 CEST 2004


Gus Tabares wrote:

> I'm trying to subclass array.array but having problems with a default
> parameter in the init constructor. Example:
> 
>     import array
> 
>     class TestClass(array.array):
>         def __init__(self, array_type = "B"):
>             array.array(array_type)
> 
> 
>>>> temp = TestClass()
> Traceback (most recent call last):
>   File "<pyshell#1>", line 1, in ?
>     temp = TestClass()
> TypeError: array() takes at least 1 argument (0 given)
> 
> I think there is something that I'm not understanding here. Any help
> is appreciated.

Seems like the argument check happens in __new__(). Try overriding that
instead:

>>> class Array(array.array):
...     def __new__(cls, tc="B"):
...             return array.array.__new__(cls, tc)
...
>>> a = Array()
>>> a
array('B')
>>> type(a)
<class '__main__.Array'>
>>>

Peter




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