为什么它打印“创建的实例数：0”而不是“创建的实例数：3”？

Question

这是垃圾邮件.py：

  class Spam:

        numInstances = 0

        def __init__(self):

            Spam.numIntances = Spam.numInstances + 1

        def printNumInstances():

            print("Number of instances created: %s" % Spam.numInstances)

这是另一个文件.py：

from spam import Spam

a = Spam()

b = Spam()

c = Spam()

Spam.printNumInstances()

a.printNumInstances()

为什么它打印“创建的实例数：0”而不是“创建的实例数：3”？

Answer 1

你有一些错别字，printNumInstances应该是一个类方法。class Spam:    numInstances = 0    def __init__(self):        Spam.numInstances = Spam.numInstances + 1    @classmethod    def printNumInstances(cls):        print("Number of instances created: %s" % cls.numInstances)a = Spam()b = Spam()c = Spam()Spam.printNumInstances()a.printNumInstances()输出：Number of instances created: 3Number of instances created: 3