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

March 2, 2022

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

>Solution :

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.