python - Python 中的多态性和构造函数行为

Question

我正在阅读 Python 中的多个构造函数多态性。我遇到了这个 code .

import sys, types, pprint

class Vector:
    """
    Demo of a class with multiple signatures for the constructor
    """
    def __init__(self, *args, **kwargs):

        if len(args) == 1:  foundOneArg = True;  theOnlyArg = args[0]
        else:               foundOneArg = False; theOnlyArg  = None

        if foundOneArg and isinstance(theOnlyArg, types.ListType):      
            self.initializeFromList(theOnlyArg)             
        elif foundOneArg and isinstance(theOnlyArg,Vector):
            self.initializeFromVector(theOnlyArg)           
        else:
            self.initializeFromArgs(*args)

        pprint.pprint(self.values)  # for debugging only

    def initializeFromList(self, argList):
        self.values = [x for x in argList]

    def initializeFromVector(self, vector):
        self.values = [x for x in vector.values]

    def initializeFromArgs(self, *args):
        self.values = [x for x in args]
#------------ end of class definition ---------------------

v = Vector(1,2,3) 
v = Vector([4,5,6]) 
q = Vector(v);

但是，我不明白initializeFromVector 的函数定义中如何设置变量vector.values。

我觉得 Python 解释器如何能够访问 vector.values 很奇怪，即使它不是在程序中手动设置的，我也不认为 values 是一个内置的-在某种变量中。

这是一个可变类的例子吗？我一直认为这种行为很奇怪。

Answer 1

这非常简单，真的:initializeFromVector 接受一个类型为vector 的参数并查找它的values 成员。这必须在构建 vector 时预先设置。

举个简单的例子:

from copy import copy

class Set(object):
    def __init__(self, other=None):
        """Initialize; optionally copy the elements of another Set."""
        self.elements = set()
        if other is not None:
            self.elements = copy(other.elements)