Python ยท Chapter 17 of 45
Python Sets
A set is an UNORDERED collection of UNIQUE items. Duplicates are automatically removed.
Create with `{1, 2, 3}` or `set([1,2,3])`. Note: `{}` is an empty DICT, not a set.
Set operations
Sets support union `|`, intersection `&`, difference `-`, and symmetric difference `^` โ exactly like math.
Common uses
De-duplicating a list, fast membership checks, and computing intersections between groups.
Example 1 (python)
nums = [1, 2, 2, 3, 3, 3]
unique = set(nums)
print(unique)Output
{1, 2, 3}set() removes duplicates from a list.
Example 2 (python)
a = {1, 2, 3}
b = {2, 3, 4}
print(a & b)
print(a | b)Output
{2, 3}
{1, 2, 3, 4}& is intersection, | is union.
Key points
- Unordered, unique items.
- `{...}` for non-empty, `set()` for empty.
- Supports set operations: `|`, `&`, `-`, `^`.
- Membership check `x in s` is very fast.
๐ก Note: `{}` creates an empty DICT. For an empty set, use `set()`.