NameError: name 'self' is not defined in Python [Solved]

# NameError: name 'self' is not defined in Python [Solved]

The "NameError: name 'self' is not defined" occurs for multiple reasons:

1. Forgetting to specify the self argument in a method.
2. Trying to use self.attribute as a default value in a method argument.
3. Trying to access self outside of a method.

Here is an example of how the error occurs.

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class Employee():
    def __init__(self, first, last=self.first):
        self.first = first
        self.last = last


# ⛔️ NameError: name 'self' is not defined
bob = Employee('bobby', 'hadz')

The issue is that we're using the self argument as a default value in the method's definition.

# Specify a default value inside the method's definition

If this is how you got the error, specify a default value inside the method's definition instead.

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class Employee():
    def __init__(self, first, last=None):
        self.first = first

        if last is None:
            self.last = self.first

bob = Employee('bobby')

print(bob.first)  # 👉️ bobby
print(bob.last)  # 👉️ bobby

We check if the last argument is None and if it is, we set it to the value of the first argument.

# Trying to access self outside of a method

You might also get the error if you try to access self outside of a method.

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class Employee():
    # ⛔️ NameError: name 'self' is not defined
    self.salary = 123

    def __init__(self, first, last=None):
        self.first = first
        self.last = last

bob = Employee('bobby')

We tried to access self directly in the class, outside of a method which caused the error.

# Declare class variables without using the self. prefix

If you meant to declare a class variable, omit the self. prefix.

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class Employee():
    # 👇️ Declare class variable
    default_salary = 123

    def __init__(self, first, last):
        self.first = first
        self.last = last

alice = Employee('alice', 'smith')
bob = Employee('bobby', 'hadz')

print(alice.default_salary)  # 👉️ 123
print(bob.default_salary)  # 👉️ 123

The class has a default_salary class variable and first and last instance variables.

Instance variables are unique to each instance you create by instantiating the class.

Regular methods get passed a self object that gives us a reference to the instance on which the method was called.

# Forgetting to specify self as an argument of a method that uses it

Another common cause of the error is forgetting to specify self as an argument of a method that uses it.

Make sure to specify self as the first argument in all class methods that make use of it.

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class Employee():
    default_salary = 123

    def __init__(self, first, last):
        self.first = first
        self.last = last

    # 👇️ Specify self as first argument
    def greet(self, greet):
        return greet + self.first + ' ' + self.last


alice = Employee('alice', 'smith')
bob = Employee('bobby', 'hadz')

print(alice.greet('hi '))  # 👉️ hi alice smith
print(bob.greet('hey '))  # 👉️ hey bobby hadz

print(alice.default_salary)  # 👉️ 123
print(bob.default_salary)  # 👉️ 123

The first and last instance variables are unique to each instance, but the instances share the same default_salary class variable.

Note that the name of the self argument is just a convention. In practice, you could use any other name, e.g. this.

However, this is not recommended as the convention is followed by most (if not all) Python developers and not following it would make your code more confusing and more difficult to read.

# Conclusion

To solve the "NameError: name 'self' is not defined", make sure:

1. You haven't forgotten to specify the self argument in a method.
2. You haven't accessed self outside of a method.
3. You haven't used the self argument as a default value of another argument in a method.