problem with set

The simple answer is that you need to use a method called split(). But let's go with the explanation.

Set

A set, as you have already been told, is an unordered data set without repetition that can contain any immutable data type, a setis also a mutable data type (unlike frozenset) but it does not allow the assignment of values ​​( item assignment) and you can't access its indices either by bracket notation ( object[index]so it's not a subscriptable object) but it can be traversed and we can also add and remove items.

Problem

When doing input('Ingrese el alfabeto 1 separado por comas: ')this you are simply asking for the values, if for example I enter Holas, que haythe result of the function it inputwill be Holas, que hayand if we convert it to a set it will give us your result, if you want to separate the values ​​by commas and obtain those separated values, use the method split()and as argument is passed the character by which the separation will be made.

c1 = input('Ingrese el alfabeto 1 separado por comas: ').split(",")
print(c1)

And we do:

Ingrese el alfabeto 1 separado por comas: a,b,c
>>> ['a','b','c']

As we can see, we no longer take the comma and we could convert that list to and we setwould obtain {'c','a','b'}(the same but disordered). Your code should go like this:

if op1 == str(2): #puedes poner "2"
         c1 = set(input('Ingrese el alfabeto 1 separado por comas: ').split(","))
         c2 = set(input('Ingrese el alfabeto 2 separado por comas: ').split(","))
         print(f'A U B: {c1 | c2}')

Observation

Now I will take a hypothetical scenario, where instead of entering letters separated by commas we enter words separated by commas. In this case it would no longer work as we thought.

c1 = set(input('Ingrese el alfabeto 1 separado por comas: ').split(","))
print(c1)

If we run and test we will get:

Ingrese el alfabeto 1 separado por comas: Holas,que,hay
>>> {'que', 'hay', 'Holas'}

Here a setbut is created according to the words that we enter, this is because when doing the separation we would be left with this: ['Holas','que','hay']and we would not have each letter separated, what we would have to do would be to eliminate the comma and make a set of the entire string complete.

#usamos el método replace para reemplazar las comas por un string vacío
c1 = set(input('Ingrese el alfabeto 1 separado por comas: ').replace(",", ""))
print(c1)

We can do that or just ask to enter the values ​​but not separated by commas :)

Note

For the ordering of setthere is no solution, the data will always be out of order, if you want to have them ordered you can use lists but of course you could no longer do set operations as you do with a set.

In a quick search I came across this result . First paragraph:

The set type in Python is the class used by the language to represent sets. A set is an unordered collection of unique elements, that is, they are not repeated.

The setthen is messy by definition.

As for the comma, it's one of the characters you entered, why wouldn't it be? From the same tutorial:

# Crea un conjunto a partir de un string
# Los caracteres repetidos se eliminan
>>> a = set('Hola Pythonista')
>>> a
{'a', 'H', 'h', 'y', 'n', 's', 'P', 't', ' ', 'i', 'l', 'o'}