How to instantiate object using iterable in Python?

Question

I need to instantiate an object using iterable with multiple objects inside. I have to create another method to do it

class MyClass:

  def __init__(self, *args):
    self.args = args

  def instantiate_from_iterable
     #some clever code

I need to have a result like this

MyClass.instantiate_from_iterable([1, 5, 3]) == MyClass(1, 5, 3)

MyClass.instantiate_from_iterable((3, 1, 7)) == MyClass(3, 1, 7)

I have no idea how to do this. If someone could help, I would appreciate it very much!

Could you provide an (abstract) example of what the result of such an instantiation would be? So how are the multiple objects inside the outtermost object positioned (nested, ...)? — CodingTil, Nov 26 '22 at 18:40
Welcome to Stack Overflow! Check out the [tour]. Your question covers the same topics as some existing ones, so I've closed it accordingly, but if there's some subtlety I'm missing, LMK (like for example, `MyClass.__eq__()` is undefined, so I'm assuming it'd be implemented as `self.args == other.args`). For more tips, check out [How to ask a good question](/help/how-to-ask). — wjandrea, Nov 26 '22 at 19:22

score 3 · Accepted Answer · edited Nov 26 '22 at 19:03

3

classmethod is what what you're after:

from collections.abc import Iterable

class MyClass:
    def __init__(self, *args):
        self.args = args
   
    @classmethod
    def instantiate_from_iterable(cls, args: Iterable):
        return cls(*args)

    
a = MyClass(1, 5, 7)
b = MyClass.instantiate_from_iterable([1, 5, 7])
     
print(a.args)  # -> (1, 5, 7)
print(b.args)  # -> (1, 5, 7)

edited Nov 26 '22 at 19:03

wjandrea

28,235
9
60
81

answered Nov 26 '22 at 18:44

Grzegorz Skibinski

12,624
2
11
34

`Iterable` is a generic, so it should have a type parameter, shouldn't it? I think `Iterable[object]` would be appropriate. – wjandrea Nov 26 '22 at 19:01

score 0 · Answer 2 · edited Nov 26 '22 at 19:19

I am not sure what you would like to do.

Try the following:

class MyClass:

    def __init__(self, *args):
        self.args = args

    
    def __eq__(self, other):
        if not isinstance(other, MyClass):
            return False
        else:
            return self.args == other.args

assert MyClass(1, 5, 3) == MyClass(*[1, 5, 3])

There would be no need for a clever function. Just unpack the list with the * before the list or tuple. You would make the object comparably using the magic function __eq__ to make them comparable.

How to instantiate object using iterable in Python?

2 Answers2