Cameron Pulsford a écrit :
Thanks, that did it! Why is that the case though? Or rather, why do the
assignments to temp.x and temp.y not effect the self.x and self.y? How
come I only run into the problem with the list?
Because there's a huge difference between binding an object to a name
and mutating an object ?
First point: Python's "assignment" is really a binding of a name and an
object _reference_ in a given namespace. Think of namespaces as
name=>object_ref dictionnaries. This implies that "assignement" never
copies anything. So when you do:
>>> list1 = []
>>> list2 = list1
the second line actually creates *another* name=>object pair referencing
the *same* list object. IOW, list1 and list2 are two named references to
a single object:
>>> list1 is list2
True
>>> id(list1) == id(list2)
True
So whether you access it thru name 'list1' or 'list2', if you mutate the
object (like append/remove/replace an element of the list), you'll see
the result thru the other name as well:
>>> list1.append('foo')
>>> list2.append('bar')
>>> list1
['foo', 'bar']
>>> list2
['foo', 'bar']
>>>
Note FWIW that list subscripting (somelist[x] = y) is really a method
call (somelist.__setitem__(x, y)) in disguise, so the same reasonning
applies.
Now *rebinding* a name is a different thing. It makes the name refer to
another object, but has no impact on other name=>object bindings
refering to the previously bound object, ie:
>>> list2 = ['hou', 'lala']
Now list2 points to a newly created list object. This doesn't impact
list1 of course:
>>> list1
['foo', 'bar']
>>> list1 is list2
False
>>> id(list1) == id(list2)
False
>>>
(snip)
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