At a loss on python scoping.
i at introo.me
Tue Mar 26 12:14:22 CET 2013
After read Dave's answer, I think I confused LEGB with attribute lookup.
So, a.r has nothing to do with LEGB.
On Tue, Mar 26, 2013 at 7:03 PM, Shiyao Ma <i at introo.me> wrote:
> 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:
>>> 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
>>> 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.)
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