Creating a list of objects in Python

Question

You demonstrate a fundamental misunderstanding.

You never created an instance of SimpleClass at all, because you didn't call it.

for count in xrange(4):
    x = SimpleClass()
    x.attr = count
    simplelist.append(x)

Or, if you let the class take parameters, instead, you can use a list comprehension.

simplelist = [SimpleClass(count) for count in xrange(4)]

To fill a list with seperate instances of a class, you can use a for loop in the declaration of the list. The * multiply will link each copy to the same instance.

instancelist = [ MyClass() for i in range(29)]

and then access the instances through the index of the list.

instancelist[5].attr1 = 'whamma'

It shouldn't be necessary to recreate the SimpleClass object each time, as some are suggesting, if you're simply using it to output data based on its attributes. However, you're not actually creating an instance of the class; you're simply creating a reference to the class object itself. Therefore, you're adding a reference to the same class attribute to the list (instead of instance attribute), over and over.

Instead of:

x = SimpleClass

you need:

x = SimpleClass()

Create a new instance each time, where each new instance has the correct state, rather than continually modifying the state of the same instance.

Alternately, store an explicitly-made copy of the object (using the hint at this page) at each step, rather than the original.

If I understand correctly your question, you ask a way to execute a deep copy of an object. What about using copy.deepcopy?

import copy

x = SimpleClass()

for count in range(0,4):
  y = copy.deepcopy(x)
  (...)
  y.attr1= '*Bob* '* count

A deepcopy is a recursive copy of the entire object. For more reference, you can have a look at the python documentation: https://docs.python.org/2/library/copy.html

I think this simply demonstrates what you are trying to achieve:

# coding: utf-8

class Class():
    count = 0
    names = []

    def __init__(self,name):
        self.number = Class.count
        self.name = name
        Class.count += 1
        Class.names.append(name)

l=[]
l.append(Class("uno"))
l.append(Class("duo"))
print l
print l[0].number, l[0].name
print l[1].number, l[1].name
print Class.count, Class.names

Run the code above and you get:-

[<__main__.Class instance at 0x6311b2c>, 
<__main__.Class instance at 0x63117ec>]
0 uno
1 duo
2 ['uno', 'duo']