Give a reference to a python instance attribute at class definition
- by Guenther Jehle
I have a class with attributes which have a reference to another attribute of this class. See class Device, value1 and value2 holding a reference to interface:
class Interface(object):
def __init__(self):
self.port=None
class Value(object):
def __init__(self, interface, name):
self.interface=interface
self.name=name
def get(self):
return "Getting Value \"%s\" with interface \"%s\""%(self.name, self.interface.port)
class Device(object):
interface=Interface()
value1=Value(interface, name="value1")
value2=Value(interface, name="value2")
def __init__(self, port):
self.interface.port=port
if __name__=="__main__":
d1=Device("Foo")
print d1.value1.get() # >>> Getting Value "value1" with interface "Foo"
d2=Device("Bar")
print d2.value1.get() # >>> Getting Value "value1" with interface "Bar"
print d1.value1.get() # >>> Getting Value "value1" with interface "Bar"
The last print is wrong, cause d1 should have the interface "Foo". I know whats going wrong: The line interface=Interface() line is executed, when the class definition is parsed (once). So every Device class has the same instance of interface.
I could change the Device class to:
class Device(object):
interface=Interface()
value1=Value(interface, name="value1")
value2=Value(interface, name="value2")
def __init__(self, port):
self.interface=Interface()
self.interface.port=port
So this is also not working: The values still have the reference to the original interface instance and the self.interface is just another instance...
The output now is:
>>> Getting Value "value1" with interface "None"
>>> Getting Value "value1" with interface "None"
>>> Getting Value "value1" with interface "None"
So how could I solve this the pythonic way? I could setup a function in the Device class to look for attributes with type Value and reassign them the new interface. Isn't this a common problem with a typical solution for it?
Thanks!
