Output:
>>> x.name = 'Fred'
>>> fred = object()
>>> fred.name = 'Fred'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'object' object has no attribute 'name'
>>> class Thing(object):
... pass
...
>>> george = Thing()
>>> george.name = 'George'
>>> george.name
'George'
So, something in the object class prevents attributes being assigned on the fly. I'm not worried about that. What confuses me is the Thing class, which inherits from object without overriding anything. Why doesn't it inherit the blocking of attributes being assigned on the fly?
Seems to me you should have received this error immediately:
Error:
>>> x.name = 'Fred'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined
>>>
here, was x already declared
>>> fred = object()
>>> type(fred)
<class 'object'>
>>> fred.name = 'Fred'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'object' object has no attribute 'name'
>>> class Thing(object):
... pass
...
>>> type(Thing)
<class 'type'>
>>> george = Thing()
>>> type(george)
<class '__main__.Thing'>
>>> george.name = 'George'
>>> type(george.name)
<class 'str'>
object does not have
__dict__ attribute, thus its instantiations can't be updated
In [1]: dir(object)
Out[1]:
['__class__',
'__delattr__',
'__dir__',
'__doc__',
'__eq__',
'__format__',
'__ge__',
'__getattribute__',
'__gt__',
'__hash__',
'__init__',
'__le__',
'__lt__',
'__ne__',
'__new__',
'__reduce__',
'__reduce_ex__',
'__repr__',
'__setattr__',
'__sizeof__',
'__str__',
'__subclasshook__']
(May-01-2017, 04:14 PM)Larz60+ Wrote: [ -> ]Seems to me you should have received this error immediately:
Error:
>>> x.name = 'Fred'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined
>>>
here, was x already declared
What was the
type of your
x
In [4]: class X(object):
...: pass
...:
In [5]: x = X()
In [6]: x.name = 'Fred'
In [7]: '__dict__' in dir(X)
Out[7]: True
Sorry, x was from previous messing around, it's not relevant to the question.
(May-01-2017, 04:16 PM)volcano63 Wrote: [ -> ]object does not have __dict__ attribute, thus its instantiations can't be updated
Okay, but then why does Thing have a dict, if Thing just inherits from object?
Maybe object is a special... object?
I tried looking it up, and the tutorial doesn't actually ever show inheriting from object...
https://docs.python.org/3/tutorial/classes.html
After googling some more, old-style classes don't exist in python 3, so
class Something(object): is exactly the same as
class Something: now.
(May-01-2017, 04:38 PM)ichabod801 Wrote: [ -> ]Okay, but then why does Thing have a dict, if Thing just inherits from object?
I presume that is the way
object.__new__ is implemented.
(May-01-2017, 04:38 PM)ichabod801 Wrote: [ -> ]Okay, but then why does Thing have a dict, if Thing just inherits from object?
According to docs, The implementation adds a few special read-only attributes to several object types, where they are relevant. Some of these are not reported by the dir() built-in function.
__dict__ is one of these.