How do I reference the variable declared under a class in Python?

Question

I am relatively new to Python and I am using Python 2.7.x

I have a question regarding namespaces in Python:

class Team():
    x = 2 
    def p(self):
        print x 

a = Team()
a.p()

When I run the code, it says global x is not defined. Shouldn't x belong to the Team object? My goal is to create a Team class where x has a default value of 2.

In Java it would be something like:

class Team()
{
    int x = 2;
}

a = new Team();

you should be calling it as `self.x` – karthikr Jan 27 '15 at 01:12 — karthikr, Jan 27 '15 at 01:12

score 5 · Accepted Answer · edited May 23 '17 at 11:57

5

If you want an instance attribute and a default value of 2 :

class Team(object): # use object for new style classes 
    def __init__(self, x=2):
        self.x = x # use self to refer to the instance

    def p(self):
        print self.x # self.x 

a = Team()
a.p()
2

b = Team(4) # give b a different value for x
b.p()
4

Difference between class vs instance attributes

new vs old style classes

edited May 23 '17 at 11:57

Community

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1

answered Jan 27 '15 at 01:19

Padraic Cunningham

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why didnt you create x at the class level ? solid answer none the less (ahh the edit makes it more clear that you are probably correctly anticipating his use case) – Joran Beasley Jan 27 '15 at 01:21
@JoranBeasley, I was going to link to an answer showing the difference between class an instance attributes, I just thought doing it this way was more obvious. – Padraic Cunningham Jan 27 '15 at 01:22
Quick note, you may want to inherit from `object` since this is on python2.x – mgilson Jan 27 '15 at 01:24
Don't forget `object` in Python 2, old-style classes are rarely used. – Ashwini Chaudhary Jan 27 '15 at 01:24
I guess I really needed to add object :) – Padraic Cunningham Jan 27 '15 at 01:27
@aceminer, no worries, there is some info worth reading in the links I added. – Padraic Cunningham Jan 27 '15 at 01:29

lqhcpsgbl · Answer 2 · 2015-01-27T01:27:08.090

1

If you want make x as class variable, just try this way:

class Team(object):
    x = 2 
    def __init__(self):
      pass

print Team.x
Team.x = 3
print Team.x

You don't need to instance to get the value and you can change it as you want.

If you want to make the num as instance property, you have to use self(like this in Java):

class Team(object):

  def __init__(self, num):
    self.num = num

  def get_num(self):
    return self.num

  def set_num(self, change_num):
    self.num = change_num

t1 = Team(2)
print t1.get_num()
t1.set_num(3)
print t1.get_num()

edited Jan 27 '15 at 01:27

answered Jan 27 '15 at 01:21

lqhcpsgbl

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Do you need __init__ explicitly if it's just passing? – Adam Hughes Jan 27 '15 at 01:44

How do I reference the variable declared under a class in Python?

2 Answers2