[Zope] Re: Unique id product

[Steve Alexander]

On 2 July, 2000 Steve Alexander wrote:
> 
> If you just want ids that are unique to a folder, try the following
> algorithm (taken originally from the Discussion object code in the PTK).
> The variable "self" is the one passed to the constructor method of a
> particular Python class, and represents the folder you want to put the
> new object into. I'm assuming the object is a "FooBar Item". The
> "foobar-%06d" bit generates a unique id for the object that looks like
> "foobar-290172837", based on the current time.
> 
>         id = int(DateTime().timeTime())
>         while hasattr(self, str(id)):
>             id = id +1
>         id = 'foobar-%09d' % id
> 
> The advantage of this approach is that there is very little contention
> in most cases.

I just looked back over some code where I used this algorithm, and I
realised that it doesn't actually work :-(  The identifiers that are
searched for do not reflect the identifiers that are produced.

The original code from the PTK does work. Here it is, adapted very
slightly:

        # Find an unused id in location
        id = int(DateTime().timeTime())
        while hasattr(self, `id`):
            id = id + 1
        return id

Here's my own, now fixed, code. Note the addition of a "max_tries"
variable.

    if id == 'auto' or id == None:
        n = int(DateTime().timeTime())
        max_tries = 10
        fk = lambda key: 'foobar-%d' % key  # function to format key
        id = fk(n)
        while max_tries and hasattr(self, str(id)):
            n = n + 1
            max_tries = max_tries-1
            id = fk(n)


Sorry for posting such rubbish the first time around :-/

--
Steve Alexander
Software Engineer
Cat-Box limited
http://www.cat-box.net