Python print and types selection

Scott David Daniels Scott.Daniels at Acm.Org
Sat Mar 28 21:47:46 CET 2009

mark.seagoe at wrote:
> ...
> It appears that if I make the class a subclass of long...
> class bignumber(long):
>     def __init__(self, initval):
>         self.val = initval
> Then if I make a new class of subclass of bignumber...
> class myclass(bignumber):
>     def __init__(self, another_custom_class)
>         bignumber.__init__(self, 0)
>         do some stuff with another_custom_class
> When I try to use this, I get an error sort of like this:
> "TypeError: long() argument must be a string or a number, not
> [whatever type another_custom_class is]"

Remember that long is an immutable class (so you need to fiddle __new__,
not __init__).  So, do something a bit more like:

     class BigNumber(long):
         def __repr__(self):
             return '%s(%s)' % (type(self).__name__, self)

     class HugeNumber(BigNumber):
         def __new__(class_, something):
             return BigNumber.__new__(class_, something * 3)

  then you can do something like:
     print 'dog = %r = %016X' % (HugeNumber(123), HugeNumber(123))

Hope that helps.

--Scott David Daniels
Scott.Daniels at Acm.Org

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