method-resolution-order Questions

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Two mixin classes specify requirements as abstract methods. Together, the classes have a full set of concrete methods. However, they fail to combine into a concrete class: no matter which order I u...

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I'm trying to use the new python dataclasses to create some mix-in classes (already as I write this I think it sounds like a rash idea), and I'm having some issues. Behold the example below: from d...

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What does mro() do? Example from django.utils.functional: for t in type(res).mro(): # <----- this if t in self.__dispatch: return self.__dispatch[t][funcname](res, *args, **kw)
Famine asked 6/1, 2010 at 3:4

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I've found myself in an unusual situation where I need to change the MRO of a class at runtime. The code: class A(object): def __init__(self): print self.__class__ print "__init__ A" self.hel...
Disarmament asked 29/12, 2013 at 6:48

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I know the title is probably a bit confusing, so let me give you an example. Suppose you have a base class Base which is intended to be subclassed to create more complex objects. But you also have ...
Posh asked 17/12, 2020 at 11:3

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I'm really confused by the following code sample: class Meta_1(type): def __call__(cls, *a, **kw): # line 1 print("entering Meta_1.__call__()") print(cls) # line 4 print(cls.mro()) # line 5 ...
Drayton asked 20/6, 2019 at 17:55

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Suppose that I have defined four classes as following: (The code has been tested on Python 3.6.5. However, I expected it should also works on Python 2.7.x with from __future__ import print_functio...
Sinkage asked 23/4, 2018 at 12:7

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In Raymond Hettinger's talk "Super considered super speak" at PyCon 2015 he explains the advantages of using super in Python in multiple inheritance context. This is one of the examples that Raymon...
Extramarital asked 4/5, 2015 at 23:23

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Consider this example where a subclass has a multi method with no signature and one with a slurpy parameter: class Foo { multi method do-it { put "Default" } multi method do-it ( Int $n ) { put ...
Turbulent asked 12/7, 2017 at 2:13

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I'm a newbie for MRO and having problem figuring out the logic for these outputs. Case 1: class A(object): def save(self): print "A" class B(A): def save(self): print "B" super(B, self).sav...
Devitalize asked 8/3, 2017 at 7:15

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Example from Raymond Hettinger's recepie class Root(object): def draw(self): # the delegation chain stops here assert not hasattr(super(Root, self), 'draw') class Shape(Root): def __init__(se...
Fawn asked 18/3, 2017 at 6:1

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Is there a difference between using super() and using the parent class name directly? For example: class Parent: def __init__(self): print("In parent") self.__a=10 class Child(Parent): def __...

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This is the code which I plan to use for my game, but it complains about an MRO error: class Player: pass class Enemy(Player): pass class GameObject(Player, Enemy): pass g = GameObject...
Hobnailed asked 23/3, 2015 at 16:4

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I have a problem with the Python MRO For this code: class F: pass class G: pass class H: pass class E(G,H): pass class D(E,F): pass class C(E,G): pass class B(C,H): pass class A(D,B,E): pass p...

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I was reading Python Multiple Inheritance (on Programiz) and then I found this StackOverflow question, Method Resolution Order (MRO) in new-style classes? but in this question some programmers like...
Emelda asked 8/11, 2016 at 2:50

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On most types/classes in Python, I can call .mro() without arguments. But not on type and its descendants: In [32]: type(4).mro() Out[32]: [int, object] In [33]: type(type(4)).mro() -------------...
Fortunna asked 18/12, 2015 at 15:20

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There are a lot of great resources on super(), including this great blog post that pops up a lot, as well as many questions on Stack Overflow. However I feel like they all stop short of explaining ...
Tyrocidine asked 22/10, 2015 at 21:15

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I'd like to know the type of an instance obtained from super() function. I tried print(super()) and __print(type(super()))__ class Base: def __init__(self): pass class Derive(Base): def __init...
Detainer asked 14/8, 2015 at 16:4

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In the book Python in a Nutshell (2nd Edition) there is an example which uses old style classes to demonstrate how methods are resolved in classic resolution order and how is it different with the ...
Stitch asked 4/12, 2009 at 17:30

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functools.singledispatch helps to define a single-dispatch generic method. Meanwhile, there is super() for calling methods or accessing attributes of a superclass. Is there something like super() ...

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I have an inheritance hierarchy whereby some of the classes have a class property named e.g., 'pickled'. I would like to get A.pickled if it exists or None if not — even if A derives from many clas...
Alissaalistair asked 10/6, 2014 at 20:53

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Given: In [37]: class A: ....: f = 1 ....: In [38]: class B(A): ....: pass ....: In [39]: getattr(B, 'f') Out[39]: 1 Okay, that either calls super or crawls the mro? In [40]: getattr(A, '...
Cipolin asked 10/6, 2014 at 21:10

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How would I sort a list of classes in Python, making sure that any child class is before any of its parent classes in the list? I ask because I want to see what type out of a list of types, an obj...
Songer asked 14/5, 2014 at 16:40

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I have two classes: class A(object): def a(self): pass class B(A): def b(self): pass print dir(A) print dir(B) How can I check from which class methods is derived in Python? For example: ...
Thirteen asked 6/4, 2014 at 18:21

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How does a super method actually works in python? In the given code: class A(object): def test(self): return 'A' class B(A): def test(self): return 'B->'+super(B, self).test() class C(...

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