[Python-Dev] inheriting basic types more efficiently (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Thu Apr 27 07:20:47 CEST 2006

Dennis Heuer wrote:

The reason why I'd like to use the long type as the base of my bitarray type is that the long type is already implemented as an array and working efficiently with large amounts of bytes.

This is wrong; you are mixing up the "is-a" and "has-a" relationships.

While it might be useful to have long as the representation of a bitarray, it's not the case that a bitarray is a long. A bitarray is a sequence type and should implement all aspects of the sequence protocol; long is a numeric type and should implement numeric operations. While the operators for these somewhat overlap (for + and *), the semantics of the operators never overlaps. So long and bitarray are completely distinct types, not subtypes of each other.

IOW, you should do

class bitarray: def init(self): self.value = 0L ...

Regards, Martin

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