method-resolution-order

问题 I am new to python. I am using python 2.7. I was going through method order resolution with a small snippet as follows: class A(object): attr = 'A' class B(A): pass class C(A): attr = 'C' class D(B,C): pass x = D() print x.attr The order of resolution is x,D,B,C,A and hence the output would be C. Going by the above example, i made a small change to the code. class A(object): attr = 'A' class E(object): attr = 'E' class B(A): pass class C(E): attr = 'C' class D(B,C): pass x = D() print x.attr

来源： https://stackoverflow.com/questions/59986413/achieving-multiple-inheritance-using-python-dataclasses

来源： https://stackoverflow.com/questions/59986413/achieving-multiple-inheritance-using-python-dataclasses

问题 This question already has answers here : How does Python's super() work with multiple inheritance? (14 answers) Closed 2 years ago . I recently experienced a TypeError , that I didn't understood when I was subclassing a QMainWindow with PyQt5 . When creating two classes: class Base (QMainWindow): def __init__(self): super(Base, self).__init__(None) class Base2 (object): def __init__(self, a, b): pass and then creating a Subclass of both, without any init arguments: class SubClass( Base, Base2

问题 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, 'f') Out[40]: 1 This is expected. In [41]: object.__getattribute__(A, 'f') Out[41]: 1 In [42]: object.__getattribute__(B, 'f') --------------------------------------------------------------------------- AttributeError Traceback (most recent call last) <ipython-input-42-de76df798d1d> in <module>() ----> 1

问题 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, 'f') Out[40]: 1 This is expected. In [41]: object.__getattribute__(A, 'f') Out[41]: 1 In [42]: object.__getattribute__(B, 'f') --------------------------------------------------------------------------- AttributeError Traceback (most recent call last) <ipython-input-42-de76df798d1d> in <module>() ----> 1

问题 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

问题 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? 回答1: 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 '

问题 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? 回答1: 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 '

问题 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 classes including e.g., B and B.pickled exists (or not). Right now my solution crawls A 's __mro__ . I would like a cleaner solution if possible. 回答1: To bypass the normal search through the __mro__ , look directly at the attribute dictionary of the class instead. You can use the vars() function for