__init__.py file

[Steven W. Orr]

On Tuesday, Apr 8th 2008 at 16:51 -0000, quoth cesco:

=>Hi,
=>
=>I need to instantiate an object (my_object) whose methods I have to
=>use in two files (file1.py and file2.py) which are in the same
=>directory. Is it possible to instantiate such object in the
=>__init__.py file and then directly use it in file1.py and file2.py?
=>If not, as I seem to experience, what is the best practice to follow
=>in this case? (I thought __init__.py was somehow useful for that).

Sounds more like a job for a singleton. I recently found one that I like a 
lot better than the standard recipe:

class Singleton(object):
    __single = None # the one, true Singleton
  
    def __new__(classtype, *args, **kwargs):
        if classtype != type(classtype.__single): 
            classtype.__single = object.__new__(classtype, *args, **kwargs)
        return classtype.__single
  
    def __init__(self,name=None):
        """Arg doesn't have to be str."""
        self.name = name
    
    def display(self):
        print self.name,id(self),type(self)

The advantage of this one is that it can be nicely subclassed.

if __name__ == "__main__":
  
    class SubSingleton(Singleton):
        def __init__(self, name=None):
            Singleton.__init__(self, name)
            self.aa = 123
            self.bb = 456
            self.cc = 789

    o1 = Singleton('foo')
    o1.display()
    o2 = Singleton('bar')
    o2.display()
    o3 = SubSingleton('foobar')
    o3.display()
    o4 = SubSingleton('barfoo')
    o4.display()
    print 'o1 = o2:',o1 == o2
    print 'o1 = o3:',o1 == o3
    print 'o3 = o4:',o3 == o4

-- 
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