pass argument for instance variable for class

Question

how can I pass argument for class's instance variable like following, how can I pass sclass for Subclass when I initial ClassElement

class Subclass(object):
    def __init__(self, arg):
        self.arg = arg


class ClassElement(object):
    sclass = Subclass('sclass')

    def __init__(self, argA: str, argB: str):
        self.argA = argA
        self.argB = argB
tcl = ClassElement('argA', 'argB')
print(tcl.argA)
print(tcl.argB)
print(tcl.sclass)
print(tcl.sclass.arg)

Your ClassElement has no attribute sclass

pstatix
– pstatix

2017-11-07 15:08:31 +00:00
Commented Nov 7, 2017 at 15:08 — pstatix
– pstatix, Commented Nov 7, 2017 at 15:08

Chen A. · Accepted Answer · 2017-11-07 19:43:09Z

1

Your code defines sclass as class variable, and you're checking an instance variable tcl.sclass.arg. These are two different things; class variables and instance variables.

If you want to use the same object to every instance - use class variable. If the object is unique to every instance - use instance variable.

Every instance has sclass:

class ClassElement(object):
    def __init__(self, argA, argB, sclass):
        self.argA = argA
        self.argB = argB
        self.sclass = Subclass(sclass)

All instances share single object (your code):

>>> ClassElement.sclass
<__main__.Subclass object at 0x02942BF0>
>>> ClassElement.sclass.arg
'sclass'

>>> tcl2 = ClassElement('argA', 'argB')
>>> id(tcl2.sclass)
43265008
>>> id(tcl.sclass)
43265008

Ok I think I understand now what you are looking for

class ClassElement(object):
    sclass = None

    def __init__(self, argA, argB, sclass):
        self.argA = argA
        self.argB = argB
        ClassElement.sclass = Subclass(sclass)

This will update the class variable with every instance creation.

edited Nov 7, 2017 at 19:43

answered Nov 7, 2017 at 15:14

Chen A.

11.5k4 gold badges55 silver badges75 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

jacobcan118 Over a year ago

hi, yes, I would like to use SUbclass as class variable but passing 'sclass' as argument when initial ClassElement...is it possible

Chen A. Over a year ago

I've edited my answer; you can accept additional parameter on ClassElement, and then pass it to your SubClass as argument.

jacobcan118 Over a year ago

but your answer is using Subclass as instance variable not using as class variable and assign now arg for sclass

Chen A. Over a year ago

So you want it to be a class or instance variable? If it's a class, once you change it - it is changed for all instances

jacobcan118 Over a year ago

yes, i try to create one @classmethod to update it, it seems like without include on def __init__, but it does nto work after include in def init

pstatix · Accepted Answer · 2017-11-07 15:11:01Z

0

class Subclass(object):
    def __init__(self, arg):
        self.arg = arg


class ClassElement(object):
    def __init__(self, argA, argB):
        self.argA = argA
        self.argB = argB
        self.sclass = Subclass('sclass')

tcl = ClassElement('argA', 'argB')

print(tcl.argA)
print(tcl.argB)
print(tcl.sclass)
print(tcl.sclass.arg)

answered Nov 7, 2017 at 15:11

pstatix

3,8884 gold badges27 silver badges48 bronze badges

Collectives™ on Stack Overflow

pass argument for instance variable for class

2 Answers 2

5 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related