Python Class Variables Or Class Variables In General
From Dive into Python: Class attributes are available both through direct reference to the class and through any instance of the class. Class attributes can be used as class-lev
Solution 1:
Because ints are immutable in python
v.counter += 1
rebinds v.counter
to a new int object. The rebinding creates an instance attribute that masks the class attribute
You can see this happening if you look at the id()
of v.counter
>>> id(v.counter)
149265780
>>> v.counter+=1
>>> id(v.counter)
149265768
Here you can see that v
now has a new attribute in its __dict__
>>> v=c()
>>> v.__dict__
{}
>>> v.counter+=1
>>> v.__dict__
{'counter': 1}
Contrast the case where counter
is mutable, eg a list
>>> class c:
... counter=[]
...
>>> v=c()
>>> v.counter+=[1]
>>> c.counter
[1]
>>>
Solution 2:
Before:
c.counter = 0
v.counter -> c.counter
During:
c.counter = 0
v.counter = c.counter + 1
After:
c.counter = 0
v.counter = 1
Solution 3:
Note that you can still get at the class value:
v.__class__.__dict__['counter']
will allow you to read or set to your class, even if you have obscured the symbol by adding a symbol to your instance's __dict__.
Solution 4:
Your are confused between declaration and instantiation.
C is the name of a class you declared.
v is an object, instantiated from c.
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