Question

I’m trying to store a file which encode an id of a class, read the file and call the class so that ->
in the files the data will be stored like

id_class:(arguments)

than the read file will look up from a list of file the right class to invoque and pass the arguments.

something like this:

class foo:
        id = 1
    def __init__(self):
        self.attr = 10
    def __str__(self):
            return str(self.attr)


class bar:
        id = 2
    def __init__(self):
        self.attr = 20
    def __str__(self):
            return str(self.attr)


def create_foo():
    return foo

def create_bar():
    return bar

class_dict = {1:create_foo(),2:create_bar()}

class_index = [1,2,1,2,1,1,1,2,2,2,1] #data read from file

class_list = [] #output list containing the newly instanciated bar or foo

for index in class_index:
    c = class_dict[index]
    class_list.append(c)

but this code append in the class_list for example foo, but is only one class, because if I modify the attribute will be modified in the whole list.

for example:

for classe in class_list:
    print classe,

print "\n-------------"
class_list[0].attr = 15

for classe in class_list:
    print classe,

the output is:

10 20 10 20 10 10 10 20 20 20 10 
-------------
15 20 15 20 15 15 15 20 20 20 15

and should be:

10 20 10 20 10 10 10 20 20 20 10 
-------------
15 20 10 20 10 10 10 20 20 20 10

Answer 1

I changed both create methods – they were missing parenthesis, without them no new instances of the object were created. Also, I changed the class_dict so it won’t call the create methods, instead I defer the instantiation to the moment the class_dict is accessed: class_dict[index](). The modified code looks like this:

class foo:
    id = 1
    def __init__(self):
        self.attr = 10

class bar:
    id = 2
    def __init__(self):
        self.attr = 20

def create_foo():
    return foo()

def create_bar():
    return bar()

class_dict = {1:create_foo,2:create_bar}

class_index = [1,2,1,2,1,1,1,2,2,2,1] #data read from file

class_list = [] #output list containing the newly instanciated bar or foo

for index in class_index:
    c = class_dict[index]()
    class_list.append(c)

for classe in class_list:
    print str(classe.attr),

print "\n-------------"
class_list[0].attr = 15

for classe in class_list:
    print str(classe.attr),