OOP - how to abort an __init__ when the initialisation code fails ?

[R.Wieser]

Rob,

> That's why if you for instance, open a serial port in an __init__ routine, 
> and something fails, you want to catch the exception there in __init__, 
> explicitly close that serial port, and reraise the exception. Otherwise 
> that port still has an object open against it until Python gets around to 
> closing it.

Thats pretty-much the situation I'm trying to jump into (Raspberry Pi, I2C 
related).

> The exception you raise should indicate why it failed, such as a TypeError 
> or ValueError if one of the arguments was some flavor of stupid, or a 
> ConnectionRefusedError.

I'll probably just play it safe, and just recast what the exception I just 
caught gave me.

> But if the concern is the try..except block around the initialization 
> catching too many things, then either a) your try block is too long and 
> encompasses too many unrelated lines of code, or b) your except condition 
> is too broad

I was thinking of (the needed) wrapping of the "newObject = classObject()" 
line in such a try..except block (to capture the re-casted exception).   I 
take it that that that means that the full contents of the __init__ block 
are wrapped too.

> or b) your except condition is too broad.  Don't "except Exception".  Only 
> catch specific exceptions where you can provide benefit by doing do.

And that means I have to study the "try ... except" methodology a bit more, 
as I've currently got only a fleeting knowledge to how it works (including 
which error classes it can selectivily catch/filter).

Regards,
Rudy Wieser