Wrong syntax when nesting 3 classes in Python?

Question

Would there be a simple way to fix this error while keeping all 3 levels?

Deriving ClassA from object does not help.

Thanks in advance!

>>> class classA:
...     class classB(object):
...         def __init__(self):
...             self.b = 3
...         class classC(classA.classB):
...             def __init__(self):
...                 super(classC, self).__init__()
...                 self.c = 4
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in classA
  File "<stdin>", line 5, in classB
NameError: name 'classA' is not defined

also, wanted to understand why thid=s does not work; maybe I miss some important concept — Yulia V
– Yulia V, Commented Jan 9, 2013 at 15:10

glglgl · Accepted Answer · 2013-01-09 16:14:26Z

8

No. At the time you define classC, classA does not exist yet.

It is only created after its body is fully executed. (The dict created from the body's execution is one parameter for the class creation call class = type('classname', (superclass_1, superclass_2, superclass_3), said_dict}).)

The easiest way would be defining them at the same level.

If absolutely needed, you can modify them later:

class classA:
    pass
class classB(object):
    def __init__(self):
        self.b = 3
class classC(classB):
    def __init__(self):
        super(classC, self).__init__()
        self.c = 4
classA.classB = classB
classB.classC = classC

edited Jan 9, 2013 at 16:14

answered Jan 9, 2013 at 15:09

glglgl

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1 Comment

Duncan Over a year ago

It might be useful to add to your answer an explanation of why classA cannot exist until all of the statements in the class body have been executed.

Facundo Casco · Accepted Answer · 2013-01-09 15:13:32Z

-1

Maybe something like this would work:

class classA:
    pass

class classB(object):
    def __init__(self):
        self.b = 3
classA.classB = classB

class classC(classA.classB):
    def __init__(self):
        super(classC, self).__init__()
        self.c = 4

classA.classB.classC = classC

answered Jan 9, 2013 at 15:13

Facundo Casco

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2 Comments

Duncan Over a year ago

Apart from makeing the last line more verbose, this doesn't add anything to @glglgl's answer.

Facundo Casco Over a year ago

@Duncan, you are right but when I posted it glglgl's answer didn't have the code

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