Python vs Java garbage collection?

[Derek Thomson]

Stuart D. Gathman wrote:
> 
> Python uses reference counting.  This is the slowest form of garbage
> collection, but it has the virtue that (apart from cycles) memory is
> released at the earliest possible moment.  

It has the advantage that it is deterministic, and therefore destructors 
can be used to manage non-memory resources, release locks and so on.

Until recently, that is. Suddenly we need to support mark-and-sweep as 
well, and so we don't have destructors any more, and need to resort to 
"close" methods.

> The problem with Python reference counting, is that it encourages sloppy
> programming like:
> 
>   data = open('myfile','r').read()
> 
> depending on the reference counting GC to release and close the file
> object immediately when read() returns.  This habit must be broken before
> Python can evolve to Lisp like speed.  The proper code:
> 
>   fp = open('myfile','r')
>   data = fp.read()
>   fp.close()

Let he who is without sin, etc.

This code is almost as sloppy. What happens if "read" throws an exception?

> 
> is not as pretty.  Perhaps some clever pythonista will invent some
> syntactic sugar to help the medicine go down.
> 

There is no way. I wish there were. This is a real problem in Java, too. 
How do I release locks and non-memory resources without adding functions 
like "close" that people have to remember to call all the time?

I understand the benefits of mark and sweep, but there is a real cost 
associated with it in terms of potential bugs and creating easy to use 
classes.

--
D.