At a loss on python scoping.

Shiyao Ma i at introo.me
Tue Mar 26 12:03:40 CET 2013


Thx, really a nice and detailed explanation.

On Tue, Mar 26, 2013 at 6:07 PM, Dave Angel <davea at davea.name> wrote:

> On 03/26/2013 02:17 AM, Shiyao Ma wrote:
>
>> Hi,
>> suppose I have a file like this:
>> class A:
>>      r = 5
>>      def func(self, s):
>>          self.s = s
>> a = A()
>> print(a.r)    # this should print 5, but where does py store the name of r
>>
>> a.func(3)
>> print(a.s)    # this should print 3, also where does py store this name.
>> what's the underlying difference between the above example?
>>
>>
> I don't think this is a scoping question at all.  These references are
> fully qualified, so scoping doesn't enter in.
>
> The class A has a dictionary containing the names of r and func.  These
> are class attributes.  Each instance has a dictionary which will contain
> the name s AFTER the A.func() is called.  Ideally such an attribute will be
> assigned in the __init__() method, in which case every instance will have s
> in its dictionary.
>
> When you use a.qqq  the attribute qqq is searched for in the instance
> dictionary and, if not found, in the class dictionary.  If still not found,
> in the parent classes' dictionary(s).
>
> You can use dir(A) and dir(a) to look at these dictionaries, but it shows
> you the combination of them, so it's not as clear.  In other words, dir(a)
> shows you both dictionaries, merged.  (Seems to me dir also sometimes
> censors some of the names, but that's a vague memory. It's never left out
> anything I cared about, so maybe it's things like single-underscore names,
> or maybe just a poor memory.)
>
>
> --
> DaveA
> --
> http://mail.python.org/**mailman/listinfo/python-list<http://mail.python.org/mailman/listinfo/python-list>
>



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