Return by reference possible?

Question

This is a simple question, but I could not find a similar one in SO. Is return by reference available in Python in anyway? (Maybe with simple hacks.)

Return by reference explanation:

def func(lst):
    return reference of lst[2] somehow

func([7, 8, 9, 10])        # returns 9
func([7, 8, 9, 10]) = 11   # lst is changed to [7, 8, 11, 10]

Is this behavior achievable? Maybe with some operator overloading?

An example of this usage in C++: Returning values by reference in C++

Answer 1

What you should probably do is just return 2 and then use that as an index into the list you passed in:

lyst = [7, 8, 9, 10]
def func(lst):
     # ...
     return 2

lyst[func(lyst)] = 11

You can create an object that encapsulates a reference to the container plus the index (or key, in the case of a dictionary) of the particular element:

class ElementRef(object):

    def __init__(self, obj, key):
        self.obj = obj
        self.key = key

    @property
    def value(self): return self.obj[self.key]

    @value.setter
    def value(self, value): self.obj[self.key] = value

Then your function looks like this:

 def func(lyst):
     # ...
     return ElementRef(lyst, 2)

And you can modify the element by setting its value attribute like this:

 func(lyst).value = 11

But I don't see a lot of value in this over just returning the index. Especially because the object can become useless if items are added to or removed from the list before it's used. Explicitly returning an index makes this an obvious problem, but if you get back an ElementRef you may assume it contains some kind of magic that it doesn't.