How to use Python 'in' operator to check my list/tuple contains each of the integers 0, 1, 2?

Using the in keyword is a shorthand for calling an object's __contains__ method.

>>> a = [1, 2, 3]
>>> 2 in a
True
>>> a.__contains__(2)
True

Thus, ("0","1","2") in [0, 1, 2] asks whether the tuple ("0", "1", "2") is contained in the list [0, 1, 2]. The answer to this question if False. To be True, you would have to have a list like this:

>>> a = [1, 2, 3, ("0","1","2")]
>>> ("0","1","2") in a
True

Please also note that the elements of your tuple are strings. You probably want to check whether any or all of the elements in your tuple - after converting these elements to integers - are contained in your list.

To check whether all elements of the tuple (as integers) are contained in the list, use

>>> sltn = [1, 2, 3]
>>> t = ("0", "2", "3")
>>> set(map(int, t)).issubset(sltn)
False

To check whether any element of the tuple (as integer) is contained in the list, you can use

>>> sltn_set = set(sltn)
>>> any(int(x) in sltn_set for x in t)
True

and make use of the lazy evaluation any performs.

Of course, if your tuple contains strings for no particular reason, just use
(1, 2, 3) and omit the conversion to int.

if ("0","1","2") in sltn

You are trying to check whether the sltn list contains the tuple ("0","1","2"), which it does not. (It contains 3 integers)

But you can get it done using #all() :

sltn = [1, 2, 3] # list
tab = ("1", "2", "3") # tuple

print(all(int(el) in sltn for el in tab)) # True