TypeError: missing 1 required positional argument: 'self'

TypeError: missing 1 required positional argument: 'self' #

The Python "TypeError: missing 1 required positional argument: 'self'" occurs when we call a method on the class instead of on an instance of the class. To solve the error, instantiate the class first and call the method on the instance, e.g. emp1.get_name().

Here is an example of how the error occurs.

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class Employee():
    def __init__(self, name, salary):
        self.name = name
        self.salary = salary

    def get_name(self):
        return self.name


# ⛔️ TypeError: Employee.get_name() missing 1 required positional argument: 'self'
print(Employee.get_name())

We called the get_name method on the Employee class rather than on an instance of Employee which caused the error.

To solve the error, instantiate the class and call the method on the instance.

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class Employee():
    def __init__(self, name, salary):
        self.name = name
        self.salary = salary

    def get_name(self):
        return self.name


# ✅ instantiate class first
emp1 = Employee('Alice', 100)

# ✅ call method on class instance
print(emp1.get_name())  # 👉️ "Alice"

We instantiated the class and called the get_name method on the instance.

When a class defines the __init__() method, the method is invoked when an instance is created.

If your class doesn't define an __init__() method, you don't have to pass any arguments when instantiating it.

Note that the first argument the __init__() method takes is self.

You could name this argument anything because the name self has no special meaning in Python.

self represents an instance of the class, so when we assign a variable as self.my_var = 'some value', we are declaring an instance variable - a variable unique to each instance.

The "TypeError: missing 1 required positional argument: 'self'" occurs because we specified the self argument in the get_name method.

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class Employee():
    def __init__(self, name, salary):
        self.name = name
        self.salary = salary

    # 👇️ specified self arg
    def get_name(self):
        return self.name


emp1 = Employee('Alice', 100)

print(emp1.get_name())  # 👉️ "Alice"

If we call the get_name method on an instance of the class, Python automatically passes self to the class method.

If your method doesn't make use of the self argument, you can declare a static method.

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class Employee():
    def __init__(self, name, salary):
        self.name = name
        self.salary = salary

    @staticmethod
    def get_name():
        return 'Alice'


print(Employee.get_name())  # 👉️ "Alice"

A static method does not receive an implicit first argument and can be called on the class or on an instance of the class.

You can also transform the method into a class method using the @classmethod decorator.

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class Employee():
    def __init__(self, name, salary):
        self.name = name
        self.salary = salary

    @classmethod
    def get_name(cls):
        print(cls)
        return 'Alice'


print(Employee.get_name())  # 👉️ "Alice"

A class method gets passed the class as an implicit first argument, just like an instance method gets passed the instance.

You can call a class method on the class (Employee.get_name()) or on an instance of the class (Employee('Alice', 100).get_name()).

If you call a class method on an instance of the class, the instance is ignored except for its class.

Conclusion #

The Python "TypeError: missing 1 required positional argument: 'self'" occurs when we call a method on the class instead of on an instance of the class. To solve the error, instantiate the class first and call the method on the instance, e.g. emp1.get_name().