Accessing the base classes of a class in a class decorator

Question

I want to disable multiple inheritance for a class, so, it could only inherit from one class. One way to do this is through a metaclass, but I want to do it using a class decorator.

class NoMultipleInheritance(type):
  def __new__(cls, name, bases, clsdict):
    if (len(bases)>1):
      raise Exception('multiple inheritance not allowed')
    
    return super().__new__(cls, name, bases, clsdict)

class B(metaclass=NoMultipleInheritance):
  pass

class C:
  pass

class A(B, C):
  pass

gives

Exception: multiple inheritance not allowed

But how do I get the base classes in a class decorator?

def no_multiple_inheritance(cls):
  # how do I get the base classes of a class here?
  return cls

class B:
  pass

class C:
  pass

@no_multiple_inheritance
class A(B, C):
  pass