self. | NameError: name 'self' is not defined or NameError: name 'foo' is not defined [duplicate]

Question

I quite often come across this object-oriented programming problem in Python, where I always seem to have both of these approaches fail. I have extensive experience with OOP in other languages, but only now using this in Python.

I want to call-upon a declared variable from __init__(self).

What is/ should be the standard approach?

Invoking self.foo:

class MyClass:
    def __init__(self):
        self.foo = 'value'

    def process():
        print(self.foo)  # !

test = MyClass()

Traceback:

NameError: name 'self' is not defined

Invoking foo:

class MyClass:
    def __init__(self):
        self.foo = 'value'  # `self.` kept here

    def process():
        print(foo)  # !

test = MyClass()

Traceback:

NameError: name 'foo' is not defined

Did you read docs.python.org/3/tutorial/classes.html already? — mkrieger1
– mkrieger1, Commented Mar 2, 2022 at 12:31

Stijn B · Accepted Answer · 2022-03-02 12:36:18Z

2

You need to pass the self argument in every method (when defined in the class) :

class MyClass:
    def __init__(self):
        self.foo = 'value'

    def process():
        print(self.foo)  # `self` is not defined,
                         # you need to give it as argument

Corrected code:

class MyClass:
    def __init__(self):
        self.foo = 'value'

    def process(self):
        print(self.foo)

answered Mar 2, 2022 at 12:36

Stijn B

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Comments

brunns · Accepted Answer · 2022-03-02 12:36:11Z

1

Neither - you want:

class MyClass:
    def __init__(self):
        self.foo = 'value'

    def process(self):
        print(self.foo)  # !

test = MyClass()
test.process()

All methods need self as an argument.

answered Mar 2, 2022 at 12:36

brunns

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1 Comment

DanielBell99 Over a year ago

To further the explanation; this is because inside of process() self.<var> needs a local declaration of self., which as you've shown should be passed.

DanielBell99 · Accepted Answer · 2022-03-02 12:36:33Z

-1

Someone had posted a comment stating:

def process(self)

Where self. needed to be added to the class method which uses any self. var/ obj.

answered Mar 2, 2022 at 12:36

DanielBell99

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