equality & comparison by default (was Re: Too many 'self' in python.That's a big flaw in this language.)

[Roy Smith]

In article <slrnf87dbp.ga2.hat at se-162.se.wtb.tue.nl>,
 "A.T.Hofkamp" <hat at se-162.se.wtb.tue.nl> wrote:

> In object oriented programming, objects are representations of values, and the
> system shouldn't care about how many instances there are of some value, just
> like numbers in math. Every instance with a certain value is the same as every
> other instance with the same value.

Whether two things are equal depends on the context.  Is one $10 note equal 
to another?  It depends.

If the context is a bank teller making change, then yes, they are equal.  
What's more, there are lots of sets of smaller notes which would be equally 
fungible.

If the context is a district attorney showing a specific $10 note to a jury 
as evidence in a drug buy-and-bust case, they're not.  It's got to be 
exactly that note, as proven by a recorded serial number.

In object oriented programming, objects are representations of the real 
world.  In one case, the $10 note represents some monetary value.  In 
another, it represents a piece of physical evidence in a criminal trial.  
Without knowing the context of how the objects are going to be used, it's 
really not possible to know how __eq__() should be defined.

Let me give you a more realistic example.  I've been doing a lot of network 
programming lately.  We've got a class to represent an IP address, and a 
class to represent an address-port pair (a "sockaddr").  Should you be able 
to compare an address to a sockaddr?  Does 192.168.10.1 == 192.168.10.1:0?  
You tell me.  This is really just the "does 1 == (1 + 0j)" question in 
disguise.  There's reasonable arguments to be made on both sides, but there 
is no one true answer.  It depends on what you're doing.