Code works in workspaces. Why am I getting this error in the challenge task?

When I run this code in workspaces, it compiles fine and I get the desired output. When I run the same code in the challenge task, I get the following error:

FAIL: test_function_code (main.TestFunctionDefinitionCode)

Traceback (most recent call last): File "", line 43, in test_function_code AssertionError: Regex didn't match: '(\{self.make\})\s(\{self.model\})' not found in 'class DreamCar:\n\tdef init(self, make, model):\n\t\tself.make = make\n\t\tself.model = model\n\t\t\n\tdef str(self):\n\t\treturn "My dream car is a {} {}.".format(self.make, self.model)' : You'll need to use self when using the attributes make and model.

Why is this?

class DreamCar:
    def __init__(self, make, model):
        self.make = make
        self.model = model

    def __str__(self):
        return "My dream car is a {} {}.".format(self.make, self.model)