IndentationError: expected an indented block after class definition on line 4

This error typically occurs in Python when there is a missing indentation after a class definition. When defining a class and its methods, it is important to indent the code that belongs to the class. Here is an example of correct indentation:

class MyClass:
    def __init__(self):
        self.my_var = "Hello World"

    def my_method(self):
        print(self.my_var)

In this example, the `__init__` method and `my_method` method are indented under the class definition. If there is no indentation, Python will raise an `IndentationError`:

class MyClass:
def __init__(self):
    self.my_var = "Hello World"

This will result in the following error message:

IndentationError: expected an indented block