如何从基类动态创建派生类

>>>new_class = type("NewClassName", (BaseClass,), {"new_method": lambda self: ...})更新任何需要它的人还应该检查 dill 项目 - 它声称能够腌制和取消腌制类就像泡菜对普通对象所做的那样，并且在我的一些测试中一直坚持下去.For example I have a base class as follows: class BaseClass(object): def __init__(self, classtype): self._type = classtypeFrom this class I derive several other classes, e.g.class TestClass(BaseClass): def __init__(self): super(TestClass, self).__init__('Test')class SpecialClass(BaseClass): def __init__(self): super(TestClass, self).__init__('Special')Is there a nice, pythonic way to create those classes dynamically by a function call that puts the new class into my current scope, like:foo(BaseClass, "My")a = MyClass()...As there will be comments and questions why I need this: The derived classes all have the exact same internal structure with the difference, that the constructor takes a number of previously undefined arguments. So, for example, MyClass takes the keywords a while the constructor of class TestClass takes b and c. inst1 = MyClass(a=4)inst2 = MyClass(a=5)inst3 = TestClass(b=False, c = "test")But they should NEVER use the type of the class as input argument likeinst1 = BaseClass(classtype = "My", a=4)I got this to work but would prefer the other way, i.e. dynamically created class objects. 解决方案 This bit of code allows you to create new classes with dynamicnames and parameter names.The parameter verification in __init__ just does not allowunknown parameters, if you need other verifications, liketype, or that they are mandatory, just add the logicthere:class BaseClass(object): def __init__(self, classtype): self._type = classtypedef ClassFactory(name, argnames, BaseClass=BaseClass): def __init__(self, **kwargs): for key, value in kwargs.items(): # here, the argnames variable is the one passed to the # ClassFactory call if key not in argnames: raise TypeError("Argument %s not valid for %s" % (key, self.__class__.__name__)) setattr(self, key, value) BaseClass.__init__(self, name[:-len("Class")]) newclass = type(name, (BaseClass,),{"__init__": __init__}) return newclassAnd this works like this, for example:>>> SpecialClass = ClassFactory("SpecialClass", "a b c".split())>>> s = SpecialClass(a=2)>>> s.a2>>> s2 = SpecialClass(d=3)Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 8, in __init__TypeError: Argument d not valid for SpecialClassI see you are asking for inserting the dynamic names in the naming scope --now, that is not considered a good practice in Python - you either havevariable names, known at coding time, or data - and names learned in runtimeare more "data" than "variables" -So, you could just add your classes to a dictionary and use them from there:name = "SpecialClass"classes = {}classes[name] = ClassFactory(name, params)instance = classes[name](...)And if your design absolutely needs the names to come in scope,just do the same, but use the dictionary returned by the globals()call instead of an arbitrary dictionary:name = "SpecialClass"globals()[name] = ClassFactory(name, params)instance = SpecialClass(...)(It indeed would be possible for the class factory function to insert the name dynamically on the global scope of the caller - but that is even worse practice, and is not compatible across Python implementations. The way to do that would be to get the caller's execution frame, through sys._getframe(1) and setting the class name in the frame's global dictionary in its f_globals attribute).update, tl;dr: This answer had become popular, still its very specific to the question body. The general answer on how to"dynamically create derived classes from a base class" in Python is a simple call to type passing the new class name, a tuple with the baseclass(es) and the __dict__ body for the new class -like this:>>> new_class = type("NewClassName", (BaseClass,), {"new_method": lambda self: ...})updateAnyone needing this should also check the dill project - it claims to be able to pickle and unpickle classes just like pickle does to ordinary objects, and had lived to it in some of my tests. 这篇关于如何从基类动态创建派生类的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！