Creating a list of objects with a class in Python

Question

I am trying to emulate a Java toString method I learned a while back. I might be off base here and there may definitely be an easier way to do what I'm trying to do with a simple list.

What I really want to do is be able to append objects to a list, and then print specific traits about those objects from the list. I also want to keep track of the index of the object. Here is what I have so far, but when I print, I get no errors, and a blank line, nothing prints.

class Character_list():
    def __init__(self, list):
        self.list = []

def toString(self):
    result = ""
    for i in self.list:
        result += self.list[i]

    return result

def main(): 
    x = Character_list([1, 2])
    print(x.toString())

main()

As self.list = [], there's nothing to be printed... You probably meant self.list = list. — Thierry Lathuille
– Thierry Lathuille, Commented Dec 24, 2018 at 21:13
Not sure what the intention is. Python classes already have a __str__ method that you can write for yourself to customise how the objects are displayed when a string representation is needed. — Robin Zigmond
– Robin Zigmond, Commented Dec 24, 2018 at 21:14
You shouldn't use list as a variable name as it clashes with the list() inbuilt function in Python. Change it to something else like char_list etc — ycx
– ycx, Commented Dec 24, 2018 at 21:24

user2390182 · Accepted Answer · 2018-12-24 21:29:09Z

Three things:

First, use the parameter you pass to the constructor to actually instantiate your object

class Character_list():
    def __init__(self, lst):
        self.lst = lst  # use the parameter! And don't use 'list' as a variable name
        # or even better, use a shallow copy:
        self.lst = list(lst)

Second, python loops are generally for-each loops. That means you are iterating elements, not indexes. So

    for i in self.lst:
        result += i

will actually append the list elements (which have to be strings, otherwise use: result += str(i)) to result.

Third, Python's version of toString is __str__ and is implicitly called when using the the built-in str() on an object. So, for instance

def __str__(self):
    return ''.join(map(str, self.lst))

will do what you intended, but more generally, e.g. when you call

print(x)

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