How to add elements from one class to another class list, python

Question

class lista(object):
    listanumere=[]
    def printer(self):
        print self.listanumere
    def adds(self,numar):
        self.listanumere.append(numar)

class movies():
    def __init__(self,ide,nume):
        self.__nume=nume
        self.__ide=ide

listarez=lista
a=movies(1,"David")
lista.adds(a)
lista.printer()

Error:

TypeError: unbound method adds() must be called with lista instance as first argument (got movies instance instead)

So my question is: How to make a class which contains a list of elements defined in another class, for example a class which contains the list of movies and some methods which modify the list for example add a new movie or remove a movie with a certain ID?

You'll need to fix the code in your __init__ method, it's unclear what the intent is there, you have several statements on the same line without indentation. — Martijn Pieters
– Martijn Pieters, Commented Nov 7, 2012 at 12:46
what do you want you lista class to do that a plain old list doesn't already do? — wim
– wim, Commented Nov 7, 2012 at 12:50

wim · Accepted Answer · 2012-11-07 12:47:26Z

6

You seem to be mixing up class methods and instance methods. You probably wanted to do:

listarez = lista()

And then

listarez.adds(a)
listarez.printer()

answered Nov 7, 2012 at 12:47

wim

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1 Comment

Lauritz V. Thaulow Over a year ago

I would also point out that listanumere is a class attribute, which means that every lista instance shares the same list, and that this might not be what OP intended. To fix, remove listanumere = [], give lista an __init__ method with self.listanumere = [] in it instead.

lucasg · Accepted Answer · 2012-11-07 12:54:12Z

Short answer :

class lista(object):
    listanumere=[]
    def printer(self):
        print "\n".join( [ str(elem)for elem in self.listanumere ] )
    def adds(self,numar):
        self.listanumere.append(numar)

class movies():
    def __init__(self,ide,nume):
        self.__nume=nume
        self.__ide=ide
    def __str__(self):
        return ":".join( [ str(self.__nume) , str(self.__ide) ] )


listarez=lista()
a=movies(1,"David")
b=movies(2,"Goliath")

listarez.adds(a)
listarez.adds(b)

listarez.printer()

If I were you, I would go with a class derived from a dictionnary (e.g. {'ID string' : movie object }) with the right overload method (init, str,..). That way you take avantage of standard methods such as itertools, etc.

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