class init takes parameters but turns them into tuples for some reason

Question

I have a very simple class:

class Item(object):
    def __init__(self, guid, sku, name):
        self.guid = guid,
        self.sku = sku,
        self.name = name

When I create an object, such as:

item1 = Item('abc123', 1, 'abc1')

And I do:

print item1.guid

I get this as an output:

('abc123',)

Instead of the expected:

'abc123'

Any idea why it does this?

P.S.: name works as expected!

What are those commas doing? You are defining tuples. Remove them! `self.guid = guid` — Moses Koledoye, Aug 28 '16 at 14:23
"PS: `name` works as expected" When you see things like this, you should be thinking, "What is different about this one?" This might have led you to the right answer in this case, since it's the only one not followed by a comma. — Two-Bit Alchemist, Aug 28 '16 at 14:26

score 18 · Answer 1 · answered Aug 28 '16 at 14:24

18

    self.guid = guid,   # Comma means create a tuple!
    self.sku = sku,
    self.name = name

You have done this yourself in your __init__ code. The tuple is constructed by a comma. Parentheses are just there to avoid ambiguity in some cases.

The correct code looks like this:

    self.guid = guid
    self.sku = sku
    self.name = name

answered Aug 28 '16 at 14:24

Two-Bit Alchemist

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What a silly mistake! Thanks (will pop your answer as 'Answer' in 9 mins when it allows me to). – emihir0 Aug 28 '16 at 14:27
1

I have spent a day trying to figure this out, thank you! – litterbugkid Feb 24 '22 at 13:29

score 6 · Answer 2 · answered Aug 28 '16 at 14:24

Python isn't doing it, you are, right here:

self.guid = guid,
self.sku = sku,

Notice those trailing commas? In python, the , is actually what constructs tuples. So guid, is saying "make a tuple of size one with guid as the element". Remove the trailing commas and you're good to go.

Unfortunately the , operator is also the argument separator in function calls and inline initialization of lists/dicts, so typically you encounter "tuple construction" as (a,b). But the () are only there to let the interpreter disambiguate between the , tuple construction operator and the , argument delimiter. If you're not in a case where there is such ambiguity, like an assignment, the , operator is all you need, even if nothing comes after it.

class __init__ takes parameters but turns them into tuples for some reason

2 Answers2

class init takes parameters but turns them into tuples for some reason