When (and why) to use del?

Duncan Booth duncan.booth at invalid.invalid
Tue Dec 9 19:55:05 CET 2008


Albert Hopkins <marduk at letterboxes.org> wrote:

>         def otherfunction():
>             try:
>                 # some stuff
>             except SomeException, e:
>                 # more stuff
>                 del e
>             return
> 
> 
> I think this looks ugly, but also does it not hurt performance by
> preempting the gc?  My feeling is that this is a misuse of 'del'. Am I
> wrong?  Is there any advantage of doing the above?
> 
It is probably a complete waste of time, but there are situations where 
code similar to this can be useful: 

        def otherfunction():
            try:
                # some stuff
            except SomeException, e:
                # more stuff
                del e
                raise
            return

The point of code like this is that when a function exits by throwing an 
exception the traceback includes a reference to the stack frame and all the 
local variables. In some situations that can result in large data 
structures not being freed for a very long time (e.g. until another 
exception is thrown that is handled at the same level). So, *in very 
specialised situations* it may be important to delete particular names from 
the local namespace.



More information about the Python-list mailing list