Python - modifying objects in a dictionary with internal methods [duplicate]

Question

I am starting with Python and struggling with populating a dictionary with class objects. My goal is to fill dictionary with device definitions and create interfaces for all devices. The problem is when I try to populate internal list with Interface class objects, all objects in the devices dictionary have the same interface definition in their lists, what is surely not right - interface definitions must be unique. In this example structure is generated for 2 devices. one of them has definition of a single interface Gi1/1, but outputs show that both devices have the same contents in the interfaces list. The source code follows:

class PE:
    interfaces = []
    def __init__(self, name):
        self.name = name
        print('creating device',self.name)

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

devices = {}
devices['bbr01'] = (PE('bbr01'))
devices['bbr02'] = (PE('bbr02'))
print('let\'s create an interface in  bbr01\'s list')
devices['bbr01'].interfaces.append(Interface('Gi1/1'))
print('what do we have in  bbr01\'s list?')
print(devices['bbr01'].interfaces[0].name)
print('what do we have in  bbr02\'s list?')
print(devices['bbr02'].interfaces[0].name)

Output:

    creating device bbr01
creating device bbr02
let's create an interface in  bbr01's list
what do we have in  bbr01's list?
Gi1/1
what do we have in  bbr02's list?
Gi1/1

The question title sounds simple enough, the question itself is pretty long winded and complicated. Could you create a MCVE by decoupling the actual problem and its nature from your specific code? — timgeb
– timgeb, Commented Mar 10, 2016 at 10:14
Sanitized most of the data fields - now it is pretty compact, and still shows the problem — Dvalin Swamp
– Dvalin Swamp, Commented Mar 10, 2016 at 10:32

Alexander Trakhimenok · Accepted Answer · 2016-03-10 11:25:14Z

0

The interfaces member is of class level, not instance.

You need to change it to:

class PE(object):
    def __init__(self, name):
        self.name = name
        self.interfaces = []
        print('creating device',self.name)

answered Mar 10, 2016 at 11:25

Alexander Trakhimenok

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