On Mon, Jun 18, 2018 at 2:48 PM, Jach Fong <jf...@ms4.hinet.net> wrote: > After looking into the \tkiniter\font.py source file, triggered by Jim's > hint on my previous subject "Why an object changes its "address" between > adjacent calls?", I get more confused. > > Below was quoted from the font.py: > ------------------------ > def nametofont(name): > """Given the name of a tk named font, returns a Font representation. > """ > return Font(name=name, exists=True) > > class Font: > """Represents a named font. > Constructor options are: > ... > exists -- does a named font by this name already exist? > Creates a new named font if False, points to the existing font if > True. > ... > """ > > def __init__(self, root=None, font=None, name=None, exists=False, > **options): > ... > ---------------------- > From my understanding, the __init__ method was called after the instance > was created, that's why the __init__ has a self parameter, right? Then, > how is it possible "...points to the existing font if True"? I didn't > see any clue in __init__ doing this. > > I also make a test of my own and it fails too. > >>>> class A: > ... objs = [] > ... def __init__(self, exists=False): > ... if exists: self = self.objs[0] > ... else: self.objs.append(self) > ... >>>> a0 = A() >>>> id(a0) > 35569968 >>>> a1 = A(exists=True) >>>> id(a1) > 35572336 > > What I expect is that id(a0) and id(a1) has the same value. They should > points to the same object.
Yes, what you want is possible; but you need a slightly different method. Assigning to 'self' doesn't do anything - it's not magical, it's just a parameter. Instead, look into overriding __new__; that's how, for instance, the int() constructor can return cached objects. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
