super（type，obj）：obj必须是typ的实例或子类型

Question

我在一个小的Django应用程序上工作，得到一个错误告诉我，super(type, obj): obj must be an instance or subtype of type。在引入函数get_object_or_404之后，我从views.py文件中获得它。下面提供的views.py文件

from django.shortcuts import render, get_object_or_404    
from django.http import HttpResponse, HttpResponseRedirect     
from django.views import View     
from .models import URL


# function based view 
def redirect_view(request, shortcode=None, *args, **kwargs):
    obj = get_object_or_404(URL, shortcode=shortcode)
    return HttpResponse("Hello World, the shortcode is {shortcode}".format(shortcode = obj.url))


# class based view 
class ShortenerView(View):

    def get(self, request, shortcode=None,  *args, **kwargs):
        obj = get_object_or_404(URL, shortcode=shortcode)
        return HttpResponse("Hello World 1, the shortcode is {shortcode}".format(shortcode = obj.url))

    def post(self, request, *args, **kwargs):
        return HttpResponse()

完整的错误信息在这里

TypeError at /b/p6jzbp/
super(type, obj): obj must be an instance or subtype of type
Request Method: GET
Request URL:    http://127.0.0.1:8000/b/p6jzbp/
Django Version: 1.11
Exception Type: TypeError
Exception Value:    
super(type, obj): obj must be an instance or subtype of type
Exception Location: /Users/Chaklader/Documents/Projects/UrlShortener/src/shortener/models.py in all, line 18

models.py中的line 18是qs_main = super(URL, self).all(*args, **kwargs)，这里是models.py文件

#  will look for the "SHORTCODE_MAX" in the settings and 
#  if not found, will put the value of 15 there 
SHORTCODE_MAX = getattr(settings, "SHORTCODE_MAX", 15)



class UrlManager(models.Manager):

    def all(self, *args, **kwargs):
        qs_main = super(URL, self).all(*args, **kwargs)
        qs      = qs_main.filter(active = True)
        return qs

    def refresh_shortcodes(self, items = None):

        qs = URL.objects.filter(id__gte=1)
        new_codes = 0

        if items is not None and isinstance(items, int):
            qs = qs.order_by('-id')[:items]

        for q in qs:
            q.shortcode = create_shortcode(q)
            print (q.id, " ", q.shortcode)
            q.save()
            new_codes += 1

        return "# new codes created {id}".format(id = new_codes)


class URL(models.Model):

    url         =  models.CharField(max_length = 220, )
    shortcode   =  models.CharField(max_length = SHORTCODE_MAX, blank = True, unique = True)
    updated     =  models.DateTimeField(auto_now = True)
    timestamp   =  models.DateTimeField(auto_now_add = True)
    active      = models.BooleanField(default = True)

    objects = UrlManager()

    def save(self, *args, **kwargs):

        if self.shortcode is  None or self.shortcode == "":
            self.shortcode = create_shortcode(self)

        super(URL, self).save(*args, **kwargs)

    def __str__(self):
        return str(self.url)

    def __unicode__(self):
        return str(self.url)

    # class Meta:
    #   ordering = '-id'

有人能给我解释一下错误的原因和解决方法吗？如果需要的话，我愿意提供更多的信息。

Answer 1

另一种可能发生此错误的方式是在Jupiter笔记本中用类重新加载模块时。

简单的解决方案是重新启动内核。

http://thomas-cokelaer.info/blog/2011/09/382/

查看@Mike W的答案了解更多细节。

Answer 2

应该使用UrlManager类作为第一个参数而不是URL模型来调用super。super不能用不相关的类/类型调用be：

从医生那里

super(type[, object-or-type]): Return a proxy object that delegates method calls to a parent or sibling class of type.

所以你不能：

>>> class D:
...    pass
... 
>>> class C:
...    def __init__(self):
...        super(D, self).__init__()
... 
>>> C()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in __init__
TypeError: super(type, obj): obj must be an instance or subtype of type

你应该：

qs_main = super(UrlManager, self).all(*args, **kwargs)

或者在Python 3中：

qs_main = super().all(*args, **kwargs)

Answer 3

在@OĝuzŞerbetci的答案中，在python3中（不仅在Jupyter中是必需的），当需要重新加载库时，例如我们将class Parent和class Child定义为

class Parent(object):
    def __init__(self):
        # do something

class Child(Parent):
    def __init__(self):
        super(self,Child).__init__(self)

如果你这样做

import library.Child
reload(library)

Child()

您将得到TypeError: super(type, obj): obj must be an instance or subtype of type，解决方案是在重新加载之后重新导入类

import library.Child
reload(library)
import library.Child

Child()