Creating separate objects in a function

Question

Creating separate objects in a function

Take a look at the following piece of code:

class MyObj(object):
    name = ""

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

v = [ {} ] * 2

def f(index):
    v[index]['surface'] = MyObj('test')
    v[index]['num'] = 3


if __name__ == '__main__':
    f(0)
    f(1)

    v[0]['num'] = 4
    print v[1]['num']

What I was expecting to get as the output of the last line is 3

; however it outputs 4

. Therefore, this should mean that a new object is always created at the same reference address.

How can I avoid this behavior? (i.e. how can I make the above code 4 prints?)

+3

python

Vito gentile May 19 '15 at 21:28

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1 answer

Padraic cunningham · Accepted Answer · 2015-05-19T21:31:05+0000

You need to create two dicts:

v = [ {},{} ]

Or use a loop:

v = [ {} for _ in range(2)]

You are creating two references to the same object.

In [2]: a = [{}] * 2

In [3]: id(a[0])
Out[3]: 140209195751176

In [4]: id(a[1])
Out[4]: 140209195751176

In [5]: a[0] is a[1]
Out[5]: True

In [6]: a = [{} for _ in range(2)]  

In [7]: id(a[1])
Out[7]: 140209198435720    

In [8]: id(a[0])
Out[8]: 140209213918728 

In [9]: a[0] is a[1]
Out[9]: False

Creating separate objects in a function

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