method-resolution-order

Why are classes being ordered this way in the MRO?

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问题 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 print(A.__mro__) I get this output: (<class '__main__.A'>, <class '__main__.D'>, <class '__main__.B'>, <class '__main__.C'>, <class '__main__.E'>, <class '__main__.G'>, <class '__main__.H'>, <class '__main__.F'>, <class 'object'>) Why do I get <class '__main__.C'> before <class '__main__.E'> ? I thought

Change python mro at runtime

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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.hello() def hello(self): print "A hello" class B(A): def __init__(self): super(B, self).__init__() print "__init__ B" self.msg_str = "B" self.hello() def hello(self): print "%s hello" % self.msg_str a = A() b = B() As to be expected, this fails as the __init__ method of A (when called from B) calls B's hello which attempts to access an attribute before it exists. The issue is that I'm constrained in the

What's the difference between super() and Parent class name?

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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 __init__(self): super().__init__() # using super() Parent.__init__(self) # using Parent class name c=Child() Is there internally a difference between super().__init__() and Parent.__init__(self) ? Willem Van Onsem Not in this case . But in general , and especially when you use multiple inheritance , super() delegates to the next object in the Method Resolution Order (MRO) as is specified in the documentation

Why “Equals” method resolution with generics differs from explicit calls

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问题 I have the following example: namespace ComparisonExample { class Program { static void Main(string[] args) { var hello1 = new Hello(); var hello2 = new Hello(); // calls Hello.Equals var compareExplicitly = hello1.Equals(hello2); // calls Object.Equals var compareWithGenerics = ObjectsEqual<Hello>(hello1, hello2); } private static bool ObjectsEqual<TValue>(TValue value1, TValue value2) { return value1.Equals(value2); } } class Hello : IEquatable<Hello> { public bool Equals(Hello other) {

Python and order of methods in multiple inheritance

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问题 In Python, if you define two classes with the same method and intend for those two classes to be parent classes, as: class A(object): def hello(self): print "hello from class a" and: class B(object): def hello(self): print "hello from class b" when you define the child class and add the two parent classes in the order A and B: class C(A, B): def __init__(self): self.hello() the method that is used when calling self.method() is the one belonging to A, or the first class in the list of

How does the order of mixins affect the derived class?

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Say, I have the following mixins that overlaps with each other by touching dispatch() : class FooMixin(object): def dispatch(self, *args, **kwargs): # perform check A ... return super(FooMixin, self).dispatch(*args, **kwargs) class BarMixin(object): def dispatch(self, *args, **kwargs): # perform check B ... return super(FooMixin, self).dispatch(*args, **kwargs) If I want my view to go through the order, check A -> check B, should my code be MyView(FooMixin, BarMixin, View) or MyView(BarMixin, FooMixin, View) ? And why do we always put View or its subclasses after mixins? (I have noticed this

How does the order of mixins affect the derived class?

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问题 Say, I have the following mixins that overlaps with each other by touching dispatch() : class FooMixin(object): def dispatch(self, *args, **kwargs): # perform check A ... return super(FooMixin, self).dispatch(*args, **kwargs) class BarMixin(object): def dispatch(self, *args, **kwargs): # perform check B ... return super(FooMixin, self).dispatch(*args, **kwargs) If I want my view to go through the order, check A -> check B, should my code be MyView(FooMixin, BarMixin, View) or MyView(BarMixin,

TypeError: Cannot create a consistent method resolution order (MRO) [duplicate]

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This question already has an answer here: Why is this an ambiguous MRO? 1 answer This is the code which I plan to use for my game. But it complains for an MRO error. I don't know why. Can someone explains for me? Many thanks. class Player: pass class Enemy(Player): pass class GameObject(Player, Enemy): pass g = GameObject() Your GameObject is inheriting from Player and Enemy . Because Enemy already inherits from Player Python now cannot determine what class to look methods up on first; either Player , or on Enemy , which would override things defined in Player . You don't need to name all base

What does “mro()” do?

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In django.utils.functional.py : for t in type(res).mro(): # <----- this if t in self.__dispatch: return self.__dispatch[t][funcname](res, *args, **kw) I don't understand mro() . What does it do and what does "mro" mean? Follow along...: >>> class A(object): pass ... >>> A.__mro__ (<class '__main__.A'>, <type 'object'>) >>> class B(A): pass ... >>> B.__mro__ (<class '__main__.B'>, <class '__main__.A'>, <type 'object'>) >>> class C(A): pass ... >>> C.__mro__ (<class '__main__.C'>, <class '__main__.A'>, <type 'object'>) >>> As long as we have single inheritance, __mro__ is just the tuple of: the

TypeError: Cannot create a consistent method resolution order (MRO) [duplicate]

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问题 This question already has an answer here: Why is this an ambiguous MRO? 1 answer This is the code which I plan to use for my game. But it complains for an MRO error. I don\'t know why. Can someone explains for me? Many thanks. class Player: pass class Enemy(Player): pass class GameObject(Player, Enemy): pass g = GameObject() 回答1: Your GameObject is inheriting from Player and Enemy . Because Enemy already inherits from Player Python now cannot determine what class to look methods up on first;