Your problem is that connect_to_imaphost is returning the new imap object but maintains no connection between that and the object that you created. They know nothing about each other.

About inheritance, the problem with inheritance is that it is "action at a distance". The behaviour of your code depends on code somewhere over there which you're not looking at right now. Tracking down cause and effect therefore becomes more tricky, and you've opened up the possibility of negative interactions between the functions that you write and the ones that the parent class depends on. That is, you've introduced tight coupling between two pieces of code that are maintained separately.

The strength of inheritance is, of course, that you can avoid writing the same code multiple times in multiple places.

Whether the advantages of inheritance outweigh the disadvantages is situation dependent, and sometimes a matter of opinion. But it is a matter of fact that many people have managed to dig themselves into deep holes using inheritance when it wasn't really appropriate.

By contrast encapsulation and information hiding has much more clear-cut benefits and more minor risks.

I'd suggest reading Code Complete 2 for more detail on this theme. (The first edition didn't cover OO, but did explain enough about encapsulation and information hiding to make it clear what the advantages are.)

In reply to Re^3: Understanding 'Multiple Inheritance' by tilly
in thread Understanding 'Multiple Inheritance' by punkish

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