[英]How to pass class keyword arguments with the `type()` built-in function?
The class
statement takes keyword arguments for various features. class
语句将关键字 arguments 用于各种功能。 For example, the __init_subclass__
function receives keyword arguments passed at the class declaration:例如,
__init_subclass__
function 接收在 class 声明中传递的关键字 arguments:
class A(object):
def __init_subclass__(cls, **kwargs):
print(f'{kwargs=}')
class B(A, my_arg=5):
pass
kwargs={'my_arg': 5}
However, doing so prevents dynamic class creation: The type
function does not seem to take the class
keyword arguments.但是,这样做会阻止动态 class 创建:
type
function 似乎没有采用class
关键字 ZDBC11CAABD5BDA99F77E6FB4E。 A factory function does , but may conflict with __init_subclass__
or similar when the factory must modify the class. 工厂 function 可以,但是当工厂必须修改 class 时,可能与
__init_subclass__
或类似内容冲突。
I would like to use the type()
built-in function in its 3-arguments version to dynamically create a class.我想在其 3 参数版本中使用
type()
内置 function 来动态创建 class。 However, there seems to be no documented way to pass keyword arguments (like my_arg
in the previous example).但是,似乎没有记录传递关键字 arguments 的方法(如前面示例中的
my_arg
)。
What would be the recommended way of doing it?推荐的方法是什么?
The bare type
is not the equivalent of class
statements in Python3.裸
type
不等同于 Python3 中的class
语句。 Use types.new_class
as a functional equivalent of class
statements.使用
types.new_class
作为class
语句的功能等效项。
class B(A, my_arg=5):
a = 12 # non-trivial class body
B = types.new_class(
'B',
# base classes of `class` statement
bases=(A,),
# keywords to the `class` statement
kwds={'my_arg': 5},
# the class body as a function
exec_body=lambda body: body.update({'a': 12}),
)
Keep in mind that a class
statement can always be wrapped in a function to allow a parameterised, functional class creation.请记住,始终可以将
class
语句包装在 function 中,以允许创建参数化的功能 class。 This also allows to set most special attributes, eg the class name via __qualname__
:这也允许通过
__qualname__
设置大多数特殊属性,例如 class 名称:
def make_b(my_arg, my_a, name=None):
class Parameterized_B(A, my_arg=my_arg):
a = my_a
if name is not None:
__qualname__ = name
return Parameterized_B
B = make_b(5, 12, "B")
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