[英]How do I use a static variable inside a class in Python
class Cls:
counter = 0
def __init__(self, name):
self.name = name
self.counter += 1
def count(self):
return self.counter
I'm learning python, what I want to have is a static counter that counts the number of times the class has been instantiated, but every time I create an instance counter
gets recreated and count()
function always returns 1. I want something that in java would look like this我正在学习 python,我想要的是一个静态计数器,它计算类被实例化的次数,但是每次我创建一个实例
counter
时都会重新创建并且count()
函数总是返回 1。我想要一些在java中看起来像这样
public class Cls {
private static int counter = 0;
private String name;
public Cls(String name) {
this.name = name;
counter ++;
}
public static int count(){
return counter;
}
}
There are two ways to access a class attribute: you can either access it directly on a class, or you can read it through self<\/code> (but not rebind it).
有两种访问类属性的方法:您可以直接在类上访问它,也可以通过
self<\/code>读取它(但不能重新绑定它)。
Accessing a class attribute through
self<\/code> won't work if there is already a value set directly on the instance so you would normally try to use the class to access a class attribute.
如果已经直接在实例上设置了值,则通过
self<\/code>访问类属性将不起作用,因此您通常会尝试使用该类来访问类属性。
class Cls:
counter = 0
def __init__(self, name):
self.name = name
Cls.counter += 1
def count(self):
return Cls.counter
Do not use Cls.不要使用 Cls。
class MyClass:
counter = 0
def __init__(self, name):
self.name = name
self.counter += 1 # this creates an instance variable counter
# thats initialized by counter if you do not set it
# it is NOT shared between instances, but specific to each
Instead you should increment the static variable:相反,您应该增加静态变量:
def __init__(self, name):
self.name = name
MyClass.counter += 1 # this increments the static class variable
If you fix如果你修复
@staticmethod
def count():
return MyClass.counter
this way, you can still call count() on instances as well as directly on the class.这样,您仍然可以在实例上以及直接在类上调用 count()。
t = MyClass("some")
print( MyClass.count() ) # fine
t1 = MyClass("other")
print( t.count() ) # only allowed if prefix the method with @staticmethod
Output:输出:
1
2
See What is the difference between @staticmethod and @classmethod in Python?请参阅Python 中的 @staticmethod 和 @classmethod 有什么区别? for further infos.
了解更多信息。
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