全局变量Python类

Question

在python中定义具有类范围的全局变量的正确方法是什么？

来自C / C ++ / Java背景我假设这是正确的：

class Shape:
    lolwut = None

    def __init__(self, default=0):
        self.lolwut = default;
    def a(self):
        print self.lolwut
    def b(self):
        self.a()

Answer 1

你所拥有的是正确的，虽然你不会把它称为全局，但它是一个类属性，可以通过类来访问，例如Shape.lolwut或通过实例例如shape.lolwut但在设置时要小心，因为它会设置实例级别属性而不是类属性

class Shape(object):
    lolwut = 1

shape = Shape()

print Shape.lolwut,  # 1
print shape.lolwut,  # 1

# setting shape.lolwut would not change class attribute lolwut 
# but will create it in the instance
shape.lolwut = 2

print Shape.lolwut,  # 1
print shape.lolwut,  # 2

# to change class attribute access it via class
Shape.lolwut = 3

print Shape.lolwut,  # 3
print shape.lolwut   # 2 

输出：

1 1 1 2 3 2

有人可能会认为输出是1 1 2 2 3 3，但这是不正确的