python class metaclass instance

Posted 2020-08-26

>>> class CObj(object):
... pass
...
>>> dir()
[‘CObj‘, ‘__builtins__‘, ‘__doc__‘, ‘__loader__‘, ‘__name__‘, ‘__package__‘, ‘__spec__‘]
>>> cob = CObj
>>> dir()
[‘CObj‘, ‘__builtins__‘, ‘__doc__‘, ‘__loader__‘, ‘__name__‘, ‘__package__‘, ‘__spec__‘, ‘cob‘]

 

>>> help(__name__)
Help on module __main__:

NAME
__main__

CLASSES
builtins.object
CObj

class CObj(builtins.object)
| Data descriptors defined here:
|
| __dict__
| dictionary for instance variables (if defined)
|
| __weakref__
| list of weak references to the object (if defined)

cob = class CObj(builtins.object)
| Data descriptors defined here:
|
| __dict__
| dictionary for instance variables (if defined)
|
| __weakref__
| list of weak references to the object (if defined)

FILE
(built-in)

>>> cins = cob()
>>> cins
<__main__.CObj object at 0x0000000000B5CC88>
>>> cins2 = CObj()
>>> cins2
<__main__.CObj object at 0x00000000013F5E10>
>>> CObj.x1 = 20
>>> cins
<__main__.CObj object at 0x0000000000B5CC88>
>>> cins.x1
20
>>> cins2.x1
20
>>> cins2.y1=30
>>> cins.y1
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: ‘CObj‘ object has no attribute ‘y1‘
>>> CObj.y1
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: type object ‘CObj‘ has no attribute ‘y1‘
>>> dir(cins)
[‘__class__‘, ‘__delattr__‘, ‘__dict__‘, ‘__dir__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__
gt__‘, ‘__hash__‘, ‘__init__‘, ‘__le__‘, ‘__lt__‘, ‘__module__‘, ‘__ne__‘, ‘__new__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__
repr__‘, ‘__setattr__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘__weakref__‘, ‘x1‘]
>>> dir(cins2)
[‘__class__‘, ‘__delattr__‘, ‘__dict__‘, ‘__dir__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__
gt__‘, ‘__hash__‘, ‘__init__‘, ‘__le__‘, ‘__lt__‘, ‘__module__‘, ‘__ne__‘, ‘__new__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__
repr__‘, ‘__setattr__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘__weakref__‘, ‘x1‘, ‘y1‘]
>>> dir(cob)
[‘__class__‘, ‘__delattr__‘, ‘__dict__‘, ‘__dir__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__
gt__‘, ‘__hash__‘, ‘__init__‘, ‘__le__‘, ‘__lt__‘, ‘__module__‘, ‘__ne__‘, ‘__new__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__
repr__‘, ‘__setattr__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘__weakref__‘, ‘x1‘]
>>> dir(CObj)
[‘__class__‘, ‘__delattr__‘, ‘__dict__‘, ‘__dir__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__
gt__‘, ‘__hash__‘, ‘__init__‘, ‘__le__‘, ‘__lt__‘, ‘__module__‘, ‘__ne__‘, ‘__new__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__
repr__‘, ‘__setattr__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘__weakref__‘, ‘x1‘]
>>>

 

 

>>> hasattr(CObj, x1)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name ‘x1‘ is not defined
>>> hasattr(CObj, ‘x1‘)
True
>>> hasattr(CObj, ‘y1‘)
False
>>> hasattr(CObj, ‘y1‘)