为什么打印“创建的实例数：0”而不是“创建的实例数：3”？

Question

这是spam.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()

为什么打印“创建的实例数：0”而不是“创建的实例数：3”？

Answer 1

您遇到了一些错别字，printNumInstances应该是一种课堂方法。

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: 3
Number of instances created: 3