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copied!<p>I think your workaround is doable; You could use properties to make access to <code>P</code>'s attributes easier:</p> <pre><code>class P(object): def __init__(self,name='default',pvar=1): self.pname = name self.pvar=pvar class C(object): def __init__(self,name,pobject=P()): #<-- The same default `P()` is # used for all instances of `C`, # unless pobject is explicitly defined. self.cname = name self.pobject=pobject @property def pvar(self): return self.pobject.pvar @pvar.setter def pvar(self,val): self.pobject.pvar=val c1=C('1') c2=C('2') </code></pre> <p><code>c1</code> and <code>c2</code> share the same <code>pobject</code>:</p> <pre><code>print(c1.pvar) # 1 c1.pvar=2 </code></pre> <p>Notice that changing <code>pvar</code> through <code>c1</code> changes <code>c2.pvar</code>:</p> <pre><code>print(c2.pvar) # 2 </code></pre> <p><code>c3</code> has a different <code>pobject</code>:</p> <pre><code>c3=C('3',P()) print(c3.pvar) # 1 </code></pre> <hr> <p>Regarding OOP design for the psychology experiment (mentioned in the comments):</p> <pre><code>import Image class Picture(object): def __init__(self,filename): self.filename = filename self.image=Image.open(filename) class Person(object): def __init__(self,name): self.name=name # other vital statistics associated with people as individuals here class Trial(object): # A trial is composed of one person, one picture, and the places they look def __init__(self,person,picture,locations): self.person=person self.picture=picture self.locations = locations # put methods for analyzing where the person looked here </code></pre> <p>A <code>Picture</code> is certainly not a <code>Person</code>, nor vice versa. And the same goes for <code>Trial</code>s. So none of these classes should inherit from each other.</p> <p>Each of these classes have a public (and maybe a private) interface. Public methods and attributes should be freely accessible from other classes. So given a <code>Trial</code> instance, <code>t</code>, the image should be accessible through <code>t.picture.image</code>. As long as you are only accessing public attributes and methods, then everything should be fine. </p> <p>For convenience, you can use <code>properties</code> to link attributes to component-attributes. For example:</p> <pre><code>class Trial(object): ... @property def image(self): return self.picture.image </code></pre> <p>But to short-cut this by making, say, <code>Trial</code> a subclass of <code>Picture</code> would be contrary to fundamental OOP design principles.</p>

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