Questions about elements in dict

[new_to_python]

Hi, I am new to Python. I came across the following example:

"Like dicts, set elements generally must be immutable. To have list-like elements, you must convert it to a tuple:"

my_data = [1, 2, 3, 4]
my_set = {tuple(my_data)}

Typing my_set gives: {(1, 2, 3, 4)}

As far as I understand, the elements of a set cannot be changed. Is the goal here to make the elements in the set list-like (changeable) via the tuple function? If so, why my_set[2] still gives an error? I don't quite understand what this example is trying to do nor the quoted statement above the python code. Anybody knows what is happening?

[stullis]

The key here is mutability. Tuples are immutable - they cannot be changed. As such, they are hashable and can be used as elements of a set. Conversely, lists are mutable and cannot be used as set elements.

my_set[2] raises an error because the set has only one element. That element, the tuple, has four elements of its own.

[new_to_python]

The key here is mutability. Tuples are immutable - they cannot be changed. As such, they are hashable and can be used as elements of a set. Conversely, lists are mutable and cannot be used as set elements.

my_set[2] raises an error because the set has only one element. That element, the tuple, has four elements of its own.

Thanks. In this case, how do I access individual element(s) in the tuple which is the only element in the dict? As far as I know, there is no ordering among the elements in a set.

[ndc85430]

Do you really want the tuple in the set, or do you actually want a set of the individual values?

In any case, you're right, the idea of ordering doesn't make sense for a set (or dict). Ordering has been sacrificed for speed - checking whether an item is in a set can be done in constant time, as opposed to linear time for an unsorted list or tuple.

[perfringo]

the idea of ordering doesn't make sense for a set (or dict).

dict part is not correct 3.6 <= Python. In 3.6 they are insertion ordered as implementation detail (What's new 3.6 >>> New dict implementation) but from 3.7 the insertion ordering is guaranteed (What's new 3.7 >>> Summary Release Highlights)

the insertion-order preservation nature of dict objects has been declared to be an official part of the Python language spec.

[new_to_python]

Do you really want the tuple in the set, or do you actually want a set of the individual values?

I am just trying to understand some concepts/examples presented in books. I guess the goal is to make the elements in the set list-like (changeable) via the tuple function. It is not clear to me how the example accomplishes that.