Python: Objects have the same value?

Question

I have a csv file which looks like this:

1;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0
2;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0
3;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0
...
16000;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0

I wrote the following Python Script:

import csv

path = 'pathToCSV.csv'
dLst = []

class Datensatz:
    #0:schluesse 1:straftat 2:gemeindeSchluessel 3:stadt 4:kreisart 5:erfassteFaelle 6:HZnachZensus
    #7:versucheAnzahl 8:versucheInProCent 9:mitSchusswaffeGedroht 10:mitSchusswaffeGeschossen=
    #11:aufgeklaerteFaelle 12:aufklaerungsquote 13:tatverdaechtigeInsgesamt 14:tatverdaechtigeM
    #15:tatverdaechtigeW 16:nichtdeutscheTatverdaechtigeAnzahl 17:NichtdeutscheTatverdaechtigeInProCent
    datensatz =['','','','','','','','','','','','','','','','','','']


def createDatensatz(row):
    d = Datensatz()
    for i in range(0,17):
        d.datensatz[i] = row[i]
    return d


def readCSV():
    with open(path, 'r', encoding = 'iso-8859-15') as csvfile:
        spamreader = csv.reader(csvfile, delimiter=';')
        for row in spamreader:
            #First print
            print(createDatensatz(row).datensatz[0])
            dLst.append(createDatensatz(row))

    for item in dLst:
        #second print
        print(item.datensatz[0])


if __name__ == "__main__":
    readCSV()

For the first print in my code, I get all numbers from 1 to 16000 which is correct!

But for the second print after adding the objects to my list I get 16000 times the last value.

Why? Where is the problem?

Datensatz.datensatz is a class member and is shared between all instances of Datensatz. You have to create an __init__ for your class and initialize instance members there. — georg
– georg, Commented Apr 14, 2017 at 2:11

unddoch · Accepted Answer · 2017-04-14 02:13:23Z

1

You need to move the definition of datensatz from the class. Right now it's a class variable shared across all instances, so it holds the last row created.

Try:

class Datensatz:
    def __init__(self):
        self.datensatz = ['','','','','','','','','','','','','','','','','','']

or better:

class Datensatz:
    def __init__(self, row):
        self.datensatz = row[:]  # [:] is making a shallow copy of the list.


def readCSV():
    with open(path, 'r', encoding = 'iso-8859-15') as csvfile:
        spamreader = csv.reader(csvfile, delimiter=';')
        for row in spamreader:
            #First print
            print(Datensatz(row).datensatz[0])
            dLst.append(Datensatz(row))

    for item in dLst:
        #second print
        print(item.datensatz[0])

answered Apr 14, 2017 at 2:13

unddoch

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