CODEWITHSUNDEEP
pythonclass
user3787291
user3787291

Reputation: 227

How to return a list instead of string from a class by default?

class A:
    def __init__(self, message):
        self.message = message

    def __repr__(self):
        return self.message

print A("Hello")

The above code prints prints "Hello", as a string is returned. But I want to return a list by default. Like if I write :

class A:
    def __init__(self, message):
        self.message = message

    def __repr__(self):
        mylist = [self.message]
        return mylist

print A("Hello")

The above code gives an error TypeError: __str__ returned non-string (type list)

I cannot create an object of the class, as i need to handle this as an exception. like:

try:
    #some code which passes parameters to constructor of A if this fails.
except A as e:
    #here I want e as a list instead of string.

Is there any way to return a list ?

Upvotes: 1

Views: 5769

Answers (3)

Arindam Roychowdhury
Arindam Roychowdhury

Reputation: 6521

Here's an idea just for fun. I am using the call for returning a non-string output. In the example below, a tuple.

class MyClass:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __add__(self, other):
        new_x = self.x + other.x
        new_y = self.y + other.y
        return MyClass(new_x, new_y)
    def __repr__(self):
        return "({},{})".format(self.x, self.y)
    def __call__(self):
        return (self.x, self.y)

Output:

>>> m1 = MyClass(10, 20)
>>> m1
(10,20)
>>> m1()
(10, 20)
>>> type(m1())
<type 'tuple'>

Upvotes: 2

Rapha&#235;l Gom&#232;s
Rapha&#235;l Gom&#232;s

Reputation: 1028

__str__ and __repr__ methods must return strings. You have to make a custom getter function.

For instance: 

class A:
    def __init__(self, message):
        self.message = message

    def get_message_as_list(self):
        return [self.message]

my_object = A("Hello")
print(my_object.get_message_as_list())

As jonrsharpe said, you can't really use a magic (double underscored) method for this.

Upvotes: 4

renefritze
renefritze

Reputation: 2243

This is a bad idea. __repr__ should always return a str because it gets used by lots of internals (like you see here in print). For info read on: https://docs.python.org/3/reference/datamodel.html#object.repr

Upvotes: 3

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