Python variables are bound to types when used?

[Diez B. Roggisch]

sjdevnull at yahoo.com wrote:
> Fredrik Lundh wrote:
> 
>>reset your brain:
>>
>>    http://effbot.org/zone/python-objects.htm
> 
> 
> Neat link.
> 
> Can you expand on this:
> 
> 
>>a type (returned by type(x))
> 
> ...
> 
>>You cannot change the type.
> 
> 
> Especially what's going on here:
> 
> 
>>>>class a(object):
> 
> ...     pass
> ...
> 
>>>>class b(a):
> 
> ...     pass
> ...
> 
>>>>x=b()
>>>>x.attr=1
>>>>type(x)
> 
> <class '__main__.b'>
> 
>>>>type(y)
> 
> <class '__main__.b'>
> 
>>>>x.__class__=a
>>>>type(x)
> 
> <class '__main__.a'>
> 
>>>>x.attr
> 
> 1
> 
> It looks to me like x is still referencing the same object (and still
> has the "attr" attribute) but its type has changed.  Is that not right?

So what? That the flexibility of python allows for such a hack has 
nothing to do with x being totally unaware of the type of the object it 
points to.

You only access values by names pointing/refering to them. If they are 
mutable, you can mutate them. If not (like strings, ints and floats), 
you have to rebind the name with a new value. But none of these changes 
what x is - and what not. Its a name, pointing to a value, and knows 
nothing about what it is actually bound to.


Regards,

Diez