Python 实用宝典

Question 1

I get some error that I can’t figure out. Any clue what is wrong with my sample code?

class B:
    def meth(self, arg):
        print arg

class C(B):
    def meth(self, arg):
        super(C, self).meth(arg)

print C().meth(1)

I got the sample test code from help of ‘super’ built-in method.

Here is the error:

Traceback (most recent call last):
  File "./test.py", line 10, in ?
    print C().meth(1)
  File "./test.py", line 8, in meth
    super(C, self).meth(arg)
TypeError: super() argument 1 must be type, not classobj

FYI, here is the help(super) from python itself:

Help on class super in module __builtin__:

class super(object)
 |  super(type) -> unbound super object
 |  super(type, obj) -> bound super object; requires isinstance(obj, type)
 |  super(type, type2) -> bound super object; requires issubclass(type2, type)
 |  Typical use to call a cooperative superclass method:
 |  class C(B):
 |      def meth(self, arg):
 |          super(C, self).meth(arg)
 |

Question 2

Your problem is that class B is not declared as a “new-style” class. Change it like so:

class B(object):

and it will work.

super() and all subclass/superclass stuff only works with new-style classes. I recommend you get in the habit of always typing that (object) on any class definition to make sure it is a new-style class.

Old-style classes (also known as “classic” classes) are always of type classobj; new-style classes are of type type. This is why you got the error message you saw:

TypeError: super() argument 1 must be type, not classobj

Try this to see for yourself:

class OldStyle:
    pass

class NewStyle(object):
    pass

print type(OldStyle)  # prints: <type 'classobj'>

print type(NewStyle) # prints <type 'type'>

Note that in Python 3.x, all classes are new-style. You can still use the syntax from the old-style classes but you get a new-style class. So, in Python 3.x you won’t have this problem.

Question 3

Also, if you can’t change class B, you can fix the error by using multiple inheritance.

class B:
    def meth(self, arg):
        print arg

class C(B, object):
    def meth(self, arg):
        super(C, self).meth(arg)

print C().meth(1)

Question 4

If the python version is 3.X, it’s okay.

I think your python version is 2.X, the super would work when adding this code

__metaclass__ = type

so the code is

__metaclass__ = type
class B:
    def meth(self, arg):
        print arg
class C(B):
    def meth(self, arg):
        super(C, self).meth(arg)
print C().meth(1)

Question 5

I was also faced by the posted issue when I used python 2.7. It is working very fine with python 3.4

To make it work in python 2.7 I have added the __metaclass__ = type attribute at the top of my program and it worked.

__metaclass__ : It eases the transition from old-style classes and new-style classes.

Python 实用宝典

super（）失败，并显示错误：当父级未从对象继承时，TypeError“参数1必须为类型，而不是classobj”

问题：super（）失败，并显示错误：当父级未从对象继承时，TypeError“参数1必须为类型，而不是classobj”

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