Subclassing array.array

[Gus Tabares]

Hello all,

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(arr ay_type)

[color=blue][color=green][color=darkred]
>>> temp = TestClass()[/color][/color][/color]
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.


Thanks,
Gus

[Larry Bates]

Re: Subclassing array.array

I think you meant to write:
class TestClass(array .array):
def __init__(self, array_type = "B"):
array.array(sel f, array_type)

Note that your "default" got gobbled upwhen
array.array was looking for first argument
to be self.

HTH,
Larry Bates
Syscon, Inc.


"Gus Tabares" <gustabares@ver izon.net> wrote in message
news:c42b7031.0 406180524.2c5d9 1fc@posting.goo gle.com...[color=blue]
> Hello all,
>
> 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(arr ay_type)
>
>[color=green][color=darkred]
> >>> temp = TestClass()[/color][/color]
> 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.
>
>
> Thanks,
> Gus[/color]

[Peter Otten]

Re: Subclassing array.array

Gus Tabares wrote:
[color=blue]
> 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(arr ay_type)
>
>[color=green][color=darkred]
>>>> temp = TestClass()[/color][/color]
> 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.[/color]

Seems like the argument check happens in __new__(). Try overriding that
instead:
[color=blue][color=green][color=darkred]
>>> class Array(array.arr ay):[/color][/color][/color]
.... def __new__(cls, tc="B"):
.... return array.array.__n ew__(cls, tc)
....[color=blue][color=green][color=darkred]
>>> a = Array()
>>> a[/color][/color][/color]
array('B')[color=blue][color=green][color=darkred]
>>> type(a)[/color][/color][/color]
<class '__main__.Array '>[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

Peter