How to make a class act as two element tuple and unpack elements?

Question

Let's say I have a following piece of code

(x1, y1), (x2, y2) = foo()

class Bar:
    def __init__(self, x, y):
        self.x = x
        self.y = y

bar1 = Bar(x1, y1)
bar2 = Bar(x2, y2)

Is there any way to avoid having x1, x2 etc and unpack is directly to Bar instance, e.g. like this:

bar1 = Bar()
bar2 = Bar()

bar1, bar2 = foo()

I would expect some magic method like:

class Bar:  
    def __init__(self):
        self.x = None
        self.y = None
    def __unpack__(self, x, y):
        self.x = x
        self.y = y

But there is no such a method (or am I wrong?). How can I accomplish it another way?

Assume that foo is given and I cannot change it to return objects directly.

are you still passing x and y in the second example of `Bar()` ? — Devesh Kumar Singh, Jun 13 '19 at 10:50
You can assign to a slice of bar (as in „mylist[:] = 1, 2, 3“) but you cannot unpack and asign in the same step-it is illdefined which elements go to „bar1“ and which go to „bar2“. — MisterMiyagi, Jun 13 '19 at 10:53
Your question is confusing. What does `bar()` do? And the question @devesh asked too. — Teshan Shanuka J, Jun 13 '19 at 10:57
@TeshanShanukaJ `bar` is an instance of `Bar`, it is not callable — hans, Jun 13 '19 at 11:16
@DeveshKumarSingh I edited the question so it is more clear now. — hans, Jun 13 '19 at 11:16
Your edit changed the behavior of foo. Does it return „x1, y1, x2, y2“ or „(x1, y1), (x2, y2)“? In the later case, you can use assignment. — MisterMiyagi, Jun 13 '19 at 11:39
You want to do something like `5=a` instead of `a=5`. That is not possible and is a wrong use of the assignment operator. — Teshan Shanuka J, Jun 13 '19 at 14:15
https://stackoverflow.com/questions/11024646/is-it-possible-to-overload-python-assignment/11024909#11024909 — Jainil Patel, Jul 26 '19 at 04:12

score 1 · Answer 1 · answered Jun 13 '19 at 11:27

1

Here's a way, but it's not particularly readable (I'm fond of tuplify though!)

def tuplify(seq, tuple_len): 
    """
    Groups elements of sequence to tuples of length tuple_len
    """
    return [tuple(el for idx, el in g[1]) for g in itertools.groupby(enumerate(seq), key=lambda x: x[0]//tuple_len)]

bar1, bar2 = (Bar(*tup) for tup in tuplify(foo(), 2)))

answered Jun 13 '19 at 11:27

Yuri Feldman

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but he want to write bar1, bar2 = foo() – Jainil Patel Jun 13 '19 at 11:32

How to make a class act as two element tuple and unpack elements?

1 Answers1