Set Comprehension — Unique Values from Comma-Separated Tokens

What you will learn

• Set syntax: {expression for name in iterable}
• Splitting on a comma delimiter
• Why duplicates disappear
• The difference from a list comprehension on the same tokens

This continues from List comprehension. Sets themselves are covered in Set creation.

The big idea

A set comprehension looks like a list comprehension, but uses curly braces and produces a set.

st = {int(val) for val in raw.split(",")}

Classroom version:

print("Enter List of Values separated by comma:")
st = {int(val) for val in input().split(",")}

Playground version — same comprehension, string instead of input():

raw = "10,2,10,4,22,2"
st = {int(val) for val in raw.split(",")}
print("Set of Element=", st)
print(type(st))

split(",") uses a comma delimiter, matching the teaching example.

Duplicates

Form	Result for 10,2,10,4
List [int(v) for v in ...]	[10, 2, 10, 4]
Set {int(v) for v in ...}	{10, 2, 4} (order not guaranteed)

The second 10 and extra 2 are stored once.

List vs set on the same data

raw = "10,2,10,4"
print([int(v) for v in raw.split(",")])
print({int(v) for v in raw.split(",")})

Use a list when order and repeats matter. Use a set when you only need unique values.

Optional if

You can still filter:

raw = "10,-3,0,22"
positives = {int(v) for v in raw.split(",") if int(v) > 0}
print(positives)

Common mistakes

Empty {} — that is a dict, not an empty set. Empty set is set().

Expecting insertion order — sets are not sequences; do not use st[0].

Forgetting split(",") — a single string "10,2" without split stays one token.

Interview cheat sheet

Question	Answer
Set comprehension braces?	{ expression for ... }
Duplicates?	Removed
Comma-separated text?	.split(",")
Type?	set

Practice in the playground

1. Change raw to "5,5,5" — the set should have one element.
2. Print len(st) vs len(lst) on the starter data.
3. Add if int(val) > 3 and see which values remain.

Next: Dict comprehension.