python 类函数有self和没有self的区别

没有self可以直接用类名调用函数，有self必须创建实例

class A:
    def __init__(self):
        self.mystr = 'hello world!'

    def helloA(self):
        print(self.mystr)


class B:
    def helloB():
        mystr = 'hello world!'
        print(mystr)

if __name__ == '__main__':
    A.helloA()

出错
Traceback (most recent call last):
File "E:/test/Python/class_self.py", line 23, in <module>
A.helloA()
TypeError: helloA() missing 1 required positional argument: 'self'
改为：

if __name__ == '__main__':
    a=A()
    a.helloA()

正确

if __name__ == '__main__':
    B.helloB()

正确