python __class__
时间: 2023-10-22 18:08:01 浏览: 64
`__class__` 是一个特殊的属性,在Python中表示一个对象所属的类。它返回对象的类对象,可以用于获取对象所属的类,并进行一些操作,比如创建新的实例。
以下是一个示例代码,演示了如何使用 `__class__` 属性:
```python
class MyClass:
pass
obj = MyClass()
print(obj.__class__) # 输出 <class '__main__.MyClass'>
new_obj = obj.__class__()
print(new_obj) # 输出 <__main__.MyClass object at 0x000001>
print(obj.__class__ is new_obj.__class__) # 输出 True,表示它们属于同一个类
```
在上面的例子中,`obj` 是 `MyClass` 类的实例,通过访问 `obj.__class__` 可以获取到该对象所属的类对象。然后,我们可以使用 `obj.__class__()` 创建一个新的实例 `new_obj`,并验证它们都属于同一个类。
需要注意的是,虽然 `__class__` 属性可以被访问和使用,但通常不建议直接使用它来创建新的实例。更好的做法是使用类名来创建新的实例,例如 `new_obj = MyClass()`。
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python _fields_
`_fields_` is a special attribute in Python that is used to define the fields of a structure or a class. It is typically used in conjunction with the `ctypes` module to define C-compatible data types in Python.
The `_fields_` attribute is a sequence of 2-tuples, where each tuple represents a single field of the structure or class. The first element of the tuple is the name of the field, and the second element is the data type of the field.
For example, consider the following code snippet:
```
import ctypes
class Point(ctypes.Structure):
_fields_ = [("x", ctypes.c_int),
("y", ctypes.c_int)]
p = Point(10, 20)
print(p.x, p.y)
```
In this example, we define a new class `Point` that inherits from the `ctypes.Structure` class. We then define the `_fields_` attribute to specify the two fields of the `Point` class: `x` (an integer) and `y` (also an integer). We then create a new instance of the `Point` class with the values (10, 20) and print out the values of the `x` and `y` fields.
Note that the `_fields_` attribute is not required for all classes, and is typically only used for classes that need to interact with C code or data structures.