由于库函数返回A，因此如果不更改它就不能使其返回B。
您可以做的一件事是编写一个函数，以获取A实例的字段并将其复制到新的B实例中：
class A: # defined by the library def __init__(self, field): self.field = fieldclass B(A): # your fancy new class def __init__(self, field, field2): self.field = field self.field2 = field2 # B has some fancy extra stuffdef b_from_a(a_instance, field2): """Given an instance of A, return a new instance of B.""" return B(a_instance.field, field2)a = A("spam") # this could be your A instance from the libraryb = b_from_a(a, "ham") # make a new B which has the data from aprint b.field, b.field2 # prints "spam ham"编辑：根据您的情况， 构图而不是继承 可能是一个不错的选择；那是您的B类可能只包含A的实例，而不是继承：
class B2: # doesn't have to inherit from A def __init__(self, a, field2): self._a = a # using composition instead self.field2 = field2 @property def field(self): # pass accesses to a return self._a.field # could provide setter, deleter, etca = A("spam")b = B2(a, "ham")print b.field, b.field2 # prints "spam ham"
