[Tutor] Borg di borg di borg (or: Swedish chef)

Peter Otten __peter__ at web.de
Mon Sep 24 12:38:33 CEST 2012

Albert-Jan Roskam wrote:

> Hi Pythonistas,
> I have three classes, Generic, Test and Test2. Generic contains a load
> method that loads a file. This may only be done once, as a file_read_open
> error is returned if the file is open already and an attempt is made to
> re-open it. The file may be opened from Test or Test2. After a lot of
> playing with a "counter" class variable, I realized this may be a
> legitimate use case for the Borg pattern
> (http://code.activestate.com/recipes/66531). Is the code below the right
> way to apply the Borg pattern?

What do you gain from that complexity? Even

assert b1.load() is b2.load()

will fail. So why not keep it simple?

_file = None
def load_file():
    global _file
    if _file is None:
        _file = open(somefile)
    return _file

(if you are using multiple threads you have to add a lock)
Of course you can bypass this "safety" measure by doing 


anywhere in your code, so it is more like a gentleman's agreement between 
you and yourself not to tread over the red line.

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