Function() argument 'code' must be code, not str

I am trying to use the ursina module, and just entered this code:

from ursina import *

class Game(Ursina):
    def __init__(self):
        pass

It generates this error:

>>> from ursina import *
>>> class Game(Ursina):
>>> ...     def __init__(self):
>>> ...
Traceback (most recent call last):
File "<test>", line 3, in <module>
class Game(Ursina):
TypeError: function() argument 'code' must be code, not str

I have no code argument, so I have no clue what this is referring to.

Can someone explain and fix this error?

See Ursina issue 579.

This is a limitation of the Ursina package which doesn't let you subclass the Ursina class.

The Ursina class is defined as:

@singleton
class Ursina(ShowBase):
    ...

And singleton is:

def singleton(cls, **kwargs):
    def getinstance(**kwargs):
        if not hasattr(cls, '_instance') or not cls._instance:
            cls._instance = cls(**kwargs)
        return cls._instance

    return getinstance

This means that the decorated Ursina is actually the function returned by singleton rather than a class, and so it can't be subclassed.