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I wonder when to use what flavour of Python 3 super().
Help on class super in module builtins:
class super(object)
| super() -> same as super(__class__, <first argument>)
| 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)
Until now I've used super() only without arguments and it worked as expected (by a Java developer).
Questions:
super(type, obj) and when super(type, type2)?Mother.__init__(...)?
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An Overview of Python's super() Function super() alone returns a temporary object of the superclass that then allows you to call that superclass's methods.
Understanding Python super() with __init__() methods When this method is called it allows the class to initialize the attributes of the class. In an inherited subclass, a parent class can be referred with the use of the super() function.
The super() function is used to give access to methods and properties of a parent or sibling class. The super() function returns an object that represents the parent class.
__new__ is static class method, while __init__ is instance method. __new__ has to create the instance first, so __init__ can initialize it. Note that __init__ takes self as parameter. Until you create instance there is no self . Now, I gather, that you're trying to implement singleton pattern in Python.
A quick note, the new usage of super is outlined in PEP3135 New Super which was implemented in python 3.0. Of particular relevance;
super().foo(1, 2)
to replace the old:
super(Foo, self).foo(1, 2)
Let's use the following classes for demonstration:
class A(object):
def m(self):
print('m')
class B(A): pass
Unbound super object doesn't dispatch attribute access to class, you have to use descriptor protocol:
>>> super(B).m
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'super' object has no attribute 'm'
>>> super(B).__get__(B(), B)
<super: <class 'B'>, <B object>>
super object bound to instance gives bound methods:
>>> super(B, B()).m
<bound method B.m of <__main__.B object at 0xb765dacc>>
>>> super(B, B()).m()
m
super object bound to class gives function (unbound methods in terms of Python 2):
>>> super(B, B).m
<function m at 0xb761482c>
>>> super(B, B).m()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: m() takes exactly 1 positional argument (0 given)
>>> super(B, B).m(B())
m
See Michele Simionato's "Things to Know About Python Super" blog posts series (1, 2, 3) for more information
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