class MyClass:
    def __init__(self, var=None):
        # The variable is optional; defaults to None
        self.var = var

# 1. Initialize without a value
obj = MyClass() 
print(obj.var)  # Output: None

# 2. Set the variable after initialization
obj.var = "Hello"
print(obj.var)  # Output: Hello

# 3. Initialize with a value
obj2 = MyClass("World")
print(obj2.var) # Output: World
