[Python-ideas] duck typing for io write methods

[Wolfgang Maier]

Nick Coghlan <ncoghlan at ...> writes:

> 
> On 13 June 2013 21:30, Wolfgang Maier
> <wolfgang.maier at ...> wrote:
> > I find it very strange that you cannot override the superclass behavior,
> > when you can override e.g. the __str__ method in any subclass of str.
> 
> If your type is acceptable input to operator.index(), you'll get the
> "initialised array of bytes" behaviour, and the custom str handling is
> triggered off a simple isinstance() check. It's part of the
> bytes/bytearray constructor definitions.
> 
> Cheers,
> Nick.
> 
> --
> Nick Coghlan   |   ncoghlan at ...   |   Brisbane, Australia
> 

ok, that's a nice technical explanation, but is that reasonable behavior?
Shouldn't Python check first to see if the object defines __bytes__() before
defaulting to the other options?

Besides, you don't have that problem with iterables (only tested inheritance
from list). A __bytes__ method seems to take priority over the default
behaviour, which is to expect the iterable to yield integers that are then
used to initialize an array of bytes.
Wolfgang