Python：如何统计创建的对象数量？

Question

I'm new to Python. My question is, what is the best way to count the number of python objects for keeping track of number of objects exist at any given time? I thought of using a static variable.

I have read several Q & A on static variables of Python, but I could not figure out how I could achieve object counting using statics.

My attempt was like this(below), from my C++ background I was expecting this to work but it didn't. Iis not iMenuNumber a static member and it should get incremented every time an object is created?

class baseMENUS:
    """A class used to display a Menu"""

    iMenuNumber = 0

    def __init__ (self, iSize):
        self.iMenuNumber = self.iMenuNumber + 1
        self.iMenuSize = iSize

def main():
   objAutoTester = baseMENUS(MENU_SIZE_1)
   ....
   ....
   ....
   objRunATest = baseMENUS(MENU_SIZE_2)

I'm yet to write the delete( del ) function(destructor).

Answer 1

Use self.__class__.iMenuNumber or baseMENUS.iMenuNumber instead of self.iMenuNumber to set the var on the class instead of the instance.

Additionally, Hungarian Notation is not pythonic (actually, it sucks in all languages) - you might want to stop using it. See http://www.python.org/dev/peps/pep-0008/ for some code style suggestions.

Answer 2

Notice that both answers above are right, but they are very different. Not only in the way you write them but in the final result.

The difference would come up if you were ever to derive from the baseMENUS class.

In nm's solution, the counter will be the same for ALL instantiations of any class derived from baseMENUS. In the case of ThiefMaster on the other hand; there will be counter for each different class derived from baseMENUS.

In the example below. I derive two classes from baseMENUS. They are AMENUS and BMENUS; I create 3 instances of AMENUS and 4 instances of BMENUS.

When I use nm's method, The counter goes all the way up to 7.

When I use ThiefMaster's I create 2 counters. One goes to 3 and the other one to 4:

class baseMENUS:
    """A class used to display a Menu"""
    iMenuNumber = 0
    jMenuNumber = 0
    def __init__ (self):
        baseMENUS.iMenuNumber = baseMENUS.iMenuNumber + 1
        self.__class__.jMenuNumber = self.__class__.jMenuNumber + 1
        self.counterNAMEOFCLASS = baseMENUS.iMenuNumber
        self.counterclass = self.__class__.jMenuNumber

class AMENUS(baseMENUS):
    def __init__(self, ):
        super(AMENUS, self).__init__()

class BMENUS(baseMENUS):
    def __init__(self, ):
        super(BMENUS, self).__init__()

allmenus = [AMENUS() for i in range(0,3)] + [BMENUS() for i in range(0,4)]
[print('Counting using n.m. method:', i.counterNAMEOFCLASS, '. And counting using ThiefMaster method :', i.counterclass) for i in allmenus]

The output created is:

Counting using n.m. method: 1 . And counting using ThiefMaster method : 1
Counting using n.m. method: 2 . And counting using ThiefMaster method : 2
Counting using n.m. method: 3 . And counting using ThiefMaster method : 3
Counting using n.m. method: 4 . And counting using ThiefMaster method : 1
Counting using n.m. method: 5 . And counting using ThiefMaster method : 2
Counting using n.m. method: 6 . And counting using ThiefMaster method : 3
Counting using n.m. method: 7 . And counting using ThiefMaster method : 4

I'm sorry to jump in 5 years late into the discussion. But I felt like this added to it.

Answer 3

I think you should use baseMENUS.iMenuNumber instead of self.iMenuNumber .

Answer 4

I would implement the following

class baseMENUS: """A class used to display a Menu"""

iMenuNumber = 0

def __init__ (self, iSize):
    baseMENUS.iMenusNumber += 1
    self.iMenuSize = iSize

def main():
   objAutoTester = baseMENUS(MENU_SIZE_1)
   ....
   ....
   ....
   objRunATest = baseMENUS(MENU_SIZE_2)

Answer 5

class obj:
count = 0
def __init__(self,id,name):
    self.id = id
    self.name = name
    obj.count +=1
    print(self.id)
    print(self.name)

o1 = obj(1,'vin')
o2 = obj(2,'bini')
o3 = obj(3,'lin')
print('object called' ,obj.count)