Python OOP object instantiation

Question

I am new to Python, and I have one dilemma concerning OOP (I am familiar with OOP concepts).
Basically, I have a class with a static class-variable (counter that shows how many objects I have instantiated):

class Employee:
   counter=0
   def __init__(self,name):
     self.name=name
     Employee.counter+=1

So now I instantiate an object:

obj1=Employee("Alan")

My question is: what happens when I have this call? What happens behind, because the static variable "counter" is incremented, but it is possible to access the object created like this?

Employee("foo")

<__main__.Employee object at 0x02A16870>

Thanks

The __init__ function is your constructor, so it increments counter whenever you create a new `Employee object. What exactly are you asking? — gen_Eric
– gen_Eric, Commented Mar 31, 2017 at 14:06
The code you've shown won't run. counter should be accessed via the instance or class — Moses Koledoye
– Moses Koledoye, Commented Mar 31, 2017 at 14:07
@MosesKoledoye: Why not? Oh, I see now... counter += 1 should be Employee.counter += 1. — gen_Eric
– gen_Eric, Commented Mar 31, 2017 at 14:07

timgeb · Accepted Answer · 2017-03-31 14:13:41Z

4

First of all, you need counter+=1 to be Employee.counter += 1 in order for the code to behave like you say it does. Otherwise you will get an error for trying to increment a variable that's not known within the scope of __init__.

Since you have no reference to Employee("foo") it will soon be garbage collected and gone forever. However, this does not change the fact that Employee.__init__ was called to increment your counter.

edited Mar 31, 2017 at 14:13

answered Mar 31, 2017 at 14:07

timgeb

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1 Comment

dejanualex Over a year ago

Yes, I forgot to put the Employee.counter += 1 . So basically since there is now reference , the garbage collector will free the heap. Thank you for theexplanation.

Yousaf · Accepted Answer · 2017-03-31 14:11:30Z

Employee("foo")

This object created above will be lost as soon as it is used and cannot be re-used whereas when you instantiate an object like

obj1=Employee("Alan")

you have a reference of that object in obj1 and it can be re-used.

My question what happens when I have this call? What happens behind

The __init__ function is the constructor and it is called each time you create a new object of your class. As this __init__ function increments the counter variable, so each time an object is created, __init__ function is called and counter gets incremented.

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