super() and @staticmethod interaction

Question

Is super() not meant to be used with staticmethods?

When I try something like

class First(object):
  @staticmethod
  def getlist():
    return ['first']

class Second(First):
  @staticmethod
  def getlist():
    l = super(Second).getlist()
    l.append('second')
    return l

a = Second.getlist()
print a

I get the following error

Traceback (most recent call last):
  File "asdf.py", line 13, in <module>
    a = Second.getlist()
  File "asdf.py", line 9, in getlist
    l = super(Second).getlist()
AttributeError: 'super' object has no attribute 'getlist'

If I change the staticmethods to classmethods and pass the class instance to super(), things work fine. Am I calling super(type) incorrectly here or is there something I'm missing?

Spannew

These should be class methods – Fitzhugh

Answer 1

The short answer to

Am I calling super(type) incorrectly here or is there something I'm missing?

is: yes, you're calling it incorrectly... AND (indeed, because) there is something you're missing.

But don't feel bad; this is an extremely difficult subject.

The documentation notes that

If the second argument is omitted, the super object returned is unbound.

The use case for unbound super objects is extremely narrow and rare. See these articles by Michele Simionato for his discussion on super():

• Things to Know About Python Super [1 of 3]
• Things to Know About Python Super [2 of 3] (this one specifically covers unbound super)
• Things to Know About Python Super [3 of 3]

Also, he argues strongly for removing unbound super from Python 3 here.

I said you were calling it "incorrectly" (though correctness is largely meaningless without context, and a toy example doesn't give much context). Because unbound super is so rare, and possibly just flat-out unjustified, as argued by Simionato, the "correct" way to use super() is to provide the second argument.

In your case, the simplest way to make your example work is

class First(object):
  @staticmethod
  def getlist():
    return ['first']

class Second(First):
  @staticmethod
  def getlist():
    l = super(Second, Second).getlist()  # note the 2nd argument
    l.append('second')
    return l

a = Second.getlist()
print a

If you think it looks funny that way, you're not wrong. But I think what most people are expecting when they see super(X) (or hoping for when they try it in their own code) is what Python gives you if you do super(X, X).

Gownsman

Is this any different in Python 3, where super() without any arguments is the usual way to call it in a regular method? I had the same problem in Python3 when calling super().foo(). – Vashti

@gerrit: Python 3's zero-argument super() only works in class or instance methods. This is due to the magic that it uses to determine which class it's being defined in. Within static methods (just as in regular, module-level functions), you still need two explicit arguments. (The single-argument form is also still unbound in Python 3.) – Gownsman

God bless you and your family – Hybridize

Answer 2

When you call a normal method on a object instance, the method receives the object instance as first parameter. It can get the class of the object and its parent class, so it makes sense to call super.

When you call a class method on an object instance or on a class, the method receives the class as first parameter. It can get the parent class, so it makes sense to call super.

But when you call a static method, the method does not receive anything and has no way to know from what object or class it was called. That's the reason why you cannot access super in a static method.

Miyamoto

Answer 3

Since Second inherits form First, you can just use First.getlist() instead of passing in two arguments in super(i.e. super(Second, Second))

class First(object):
   @staticmethod
   def getlist():
     return ['first']

class Second(First):
  @staticmethod
  def getlist():
    # l = super(Second, Second).getlist()
    l = First.getlist()
    l.append('second')
    return l

a = Second.getlist()
print (a)

Rapallo

However, this can get screwed up if you later change the ancestry. For example, if an intermediate class OnePointFive is added in the inheritance tree in between First and Second, Second will skip a level when calling what used to be its super. – Lemma