类的python元素复制了accros新实例

Question

我有一个名为KSlamComp的类，它从文件中读取数字并将其放入两个属性gt_raw和slam_raw

class KSlamComp:
    def __init__(self, forward_nodes_lookup = 1, backward_nodes_lookup = 0, slam_input_raw = data.Data(), gt_input_raw = data.Data()):
        self.slam_raw = slam_input_raw
        self.gt_raw = gt_input_raw
        self.nb_node_forward = forward_nodes_lookup
        self.nb_node_backward = backward_nodes_lookup

    def read(self, file_name):
        assert(len(self.slam_raw.posetime) == 0)
        f = open(file_name, 'r')
        for line in f:
            print("line")
            assert len(line.split()) == 8

            slampose = data.Pose(data.Point( float(line.split()[0]), float(line.split()[1] )),  float(line.split()[2]))
            gtpose = data.Pose(data.Point( float(line.split()[4]), float(line.split()[5] )),  float(line.split()[6]))

            self.slam_raw.posetime.append( (slampose, float(line.split()[3]) ) )
            self.gt_raw.posetime.append( (gtpose, float(line.split()[7]) ) )


    def printraw(self):
        print("Printing Raw data")
        for x in range(0, len(self.slam_raw.posetime)):
            print(str(self.slam_raw.posetime[x][0].getPosition().x) + " " \
                + str(self.slam_raw.posetime[x][0].getPosition().y) + " " \
                + str(self.slam_raw.posetime[x][0].getOrientation()) + " " \
                + str(self.slam_raw.posetime[x][1]) + " " + \
                  str(self.gt_raw.posetime[x][0].getPosition().x) + " " \
                + str(self.gt_raw.posetime[x][0].getPosition().y) + " " \
                + str(self.gt_raw.posetime[x][0].getOrientation()) + " " \
                + str(self.gt_raw.posetime[x][1]))
        print("\n")

Data就是这样的东西

class Data:
    def __init__(self):
        #Tuple with pose and time 
        self.posetime = list()

现在我有了这个测试文件

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

from kslamcomp import data
from kslamcomp import kslamcomp

def main():
    # parse command line options
    d = kslamcomp.KSlamComp(1, 0)
    d.read("data_files/shifted.txt")
    d.printraw()
    d.print()

    d_invert = kslamcomp.KSlamComp()
    d_invert.printraw()
    d.printraw()

if __name__ == "__main__":
    main()

我的理解是，du invert是一个新对象KSlamComp，所有属性都初始化为它们的默认值。尤其是，self.slam_raw和self.gt_raw是具有空列表的空Data对象。不管我什么时候运行这个程序

$ python3 test_sanity.py 
line
line
line
line
Printing Raw data
1.0 1.0 1.0 2.0 3.0 3.0 3.0 6.0
5.0 5.0 5.0 6.0 8.0 8.0 7.1 14.0
9.0 9.0 9.0 10.0 11.0 11.0 11.0 2.0
13.0 13.0 13.0 14.0 15.0 15.0 15.0 10.0


Printing Raw data
1.0 1.0 1.0 2.0 3.0 3.0 3.0 6.0
5.0 5.0 5.0 6.0 8.0 8.0 7.1 14.0
9.0 9.0 9.0 10.0 11.0 11.0 11.0 2.0
13.0 13.0 13.0 14.0 15.0 15.0 15.0 10.0


Printing Raw data
1.0 1.0 1.0 2.0 3.0 3.0 3.0 6.0
5.0 5.0 5.0 6.0 8.0 8.0 7.1 14.0
9.0 9.0 9.0 10.0 11.0 11.0 11.0 2.0
13.0 13.0 13.0 14.0 15.0 15.0 15.0 10.0

虽然我认为第二个打印应该是空的，但它似乎包含在第一个KSlamComp对象中读取的数据

为什么两个对象中的slef.gt_raw和Self.slam_raw是同一个对象？如果我通过调用d_invert = kslamcomp.KSlamComp(0, 1, data.Data(), data.Data())来“手动”初始化它们，这似乎是可行的，但我认为使用默认参数也是一样的

Answer 1

不应将可变对象用作函数的默认值，因为默认值存储在函数对象中。 我可能会写信

class KSlamComp:
    def __init__(..., slam_input_raw = None, gt_input_raw = None, ...) 
        self.slam_raw = slam_input_raw or data.Data()
        self.gt_stuff = gt_input_raw or data.Data()