[Python-Dev] inheriting basic types more efficiently
"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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