On 2015-08-24 06:49, 344276105 wrote:
Hi all, I am a python learner. I encountered a problem when i was testing the following code. What is strange is that if I replace the object name with zhang, the program would be ok. And if I replace the Person.population with self.__class__.population, it will also be ok. So what is the matter? Here is the code,#!/usr/bin/python # Filename: objvar.py class Person: population = 0 def __init__(self, name): self.name = name print '(Initializing %s...)' % self.name Person.population += 1 def __del__(self): print '%s says bye.' % self.name Person.population -= 1 if Person.population == 0: print 'I am the last one.' else: print 'There are still %d people left.' % Person.population def sayHi(self): print 'Hi, my name is %s.' % self.name def howMany(self): if Person.population == 1: print 'I am the only person here.' else: print 'We have %d persons here.' % Person.population zhangsan = Person('Swaroop') zhangsan.sayHi() zhangsan.howMany() lisi = Person('LiSi') lisi.sayHi() lisi.howMany() zhangsan.sayHi() zhangsan.howMany()
The error occurs because the program has finished and Python is cleaning up. Unfortunately, it looks like when the __del__ methods run, the Person class has already been cleaned up (Person is None at that point). It looks like that behaviour was fixed in Python 3.2. By the way, it's recommended that you use the latest version of Python 3 unless you require Python 2 because of some dependency on something that doesn't (yet?) work on Python 3. -- https://mail.python.org/mailman/listinfo/python-list
